OPINION
The Federal Deposit Insurance Corporation (“FDIC”), as receiver for NetBank, FSB (“NetBank”),3 appeals the bankruptcy *819court’s grant of summary judgment in favor of the chapter 7 trustee, avoiding Net-Bank’s security interest in rights to future payments due under various leases (“lease payments”) and in contract rights under the surety bonds guaranteeing the lease payments.4 At issue in the appeal before us is whether NetBank perfected its security interests in the lease payments and the surety bonds so as to withstand the trustee’s avoidance powers under §§ 544 and 547(b).
For the reasons set forth below, we AFFIRM.
I. FACTS
A. Events Prior to the Bankruptcy
The present appeal is the second appeal in the underlying adversary proceeding. Although we set forth substantial factual background in NetBank, FSB v. Kipperman (In re Commercial Money Center, Inc.), 350 B.R. 465 (9th Cir. BAP 2006) (“Commercial Money Center I ”), we reiterate certain pertinent facts here for convenience of reference.
1. Sale and Servicing Agreement between CMC and NetBank
Commercial Money Center, Inc. (“CMC”) engaged in the business of originating commercial equipment leases. CMC purchased equipment and leased it to consumer end-users with sub-prime credit. CMC then grouped these leases together into “lease pools” and assigned the lease payments (but not the leases themselves) to third-party investors. To enhance the marketability of the lease pools, CMC obtained surety bonds guaranteeing the lease payments and assigned its rights under the surety bonds to the investors.
Between March 18, 1999 and September 6, 2000, NetBank paid CMC approximately $47 million for seven lease pools.5 With respect to each of the seven lease pools, CMC, NetBank and Amwest Surety Insurance Company (“Amwest”) entered into a separate Sale and Servicing Agreement (“SSA”).6 Amwest initially issued the surety bonds, but its successor, Royal Indemnity Company (“Royal”), issued its own surety bonds to replace them.
Under the SSA, CMC assigned to Net-Bank its rights to and interests in the lease payments and its rights under the surety bonds, among other things (collectively, “transferred assets”). SSA, Article II, § 2.1(a)(i)-(iv). As security for the lease payments, CMC granted NetBank a security interest in a bundle of assets, including the leases themselves, the equipment, insurance policies, and all items contained in the lease files, and any other documents relating to the leases kept on file pursuant to CMC’s customary procedures (collectively, “lease assets”) — but not the surety bonds. SSA, Article II, § 2.1(b)(i).
*820At the time CMC assigned the transferred assets and granted the security interest in the lease assets to NetBank, CMC represented that all filings and other actions required to give NetBank a first priority perfected lien or ownership interest in the leases and the transferred assets had been accomplished, including filings of Uniform Commercial Code (“UCC”) financing statements. SSA, Article II, § 2.4(n). CMC also agreed that it would take all actions necessary to maintain and/or preserve, in NetBank’s favor, a first priority perfected security interest in the lease assets and the transferred assets. SSA, Article II, § 3.13(b)-(e); Article VI, § 6.5; Article X, § 10.2(a). Neither CMC nor NetBank filed any UCC financing statements with respect to the lease assets or the transferred assets.
Pursuant to the SSA, Royal was appointed as servicer, and CMC was appointed as sub-servicer. SSA, Article I, § 1.1.
As sub-servicer, CMC assumed all responsibility, as agent for and on behalf of the servicer, to perform the servicer’s duties under the SSA, although the servi-cer was not relieved of any of its obligations under the SSA. SSA, Article I, § 1.1; Article III, § 3.7. NetBank agreed to deal directly with CMC for as long as it served as sub-servicer. SSA, Article III, § 3.7. CMC later formed Commercial Servicing Corporation (“CSC”) to service the lease pools. CSC was a wholly-owned subsidiary of CMC.
The servicer and/or sub-servicer acted as NetBank’s agent. SSA, Article II, § 2.2(a); Article III, § 3.1. As agent, the servicer and/or sub-servicer was to manage the leases and collect and distribute the lease payments, among other things. SSA, Article III, § 3.1; Article III, § 3.2(a).
The servicer and/or sub-servicer also acted as NetBank’s custodian of documents and instruments relating to the leases. SSA, Article II, § 2.2(a). Specifically, the servicer and/or sub-servicer was to be in possession and maintain custody of the original leases, all documents relating to the leases and copies of all of the surety bonds, among other things. SSA, Article II, § 2.2(a)(i)-(iv); Article II, § 2.2(c)(i)-(iii). CMC was to hold and maintain the lease files in its offices in Escondido, California. SSA, Article II, § 2.2(b). Royal agreed to deliver the original lease files to CMC as sub-servicer, though CMC was to deliver the original surety bonds to Net-Bank. SSA, Article II, § 2.7(a)-(b).
CMC retained physical possession of the lease files at its offices. NetBank actually had physical possession of the surety bonds.
2. District Court proceedings
In late 2001 and early 2002, CMC failed to distribute the payments owed to Net-Bank under the SSAs. NetBank demanded compensation from Royal as surety for the defaulted payments; Royal complied.
On February 1, 2002, Royal initiated an action against CMC in the United States District Court for the Southern District of California (“District Court Action”),7 seeking to freeze certain bank accounts of CMC, remove CMC as sub-servicer and obtain an order requiring CMC to provide an accounting of the books and financial records of the Royal bonded leases.
On the same day, Royal obtained a temporary restraining order (“TRO”) against CMC, requiring CMC to “make available *821to Royal all books, records, and accounts related to Royal bonded leases.” CMC also was prohibited from withdrawing or transferring any Royal bonded lease payments.
Between February 11, 2002 and March 26, 2002, Royal and CMC stipulated to several amendments to the TRO,8 all of which required CMC to “make reasonably available” to Royal, beginning on February 6, 2002, all books, records and accounts related to Royal’s bonded leases. Royal initially did not seek possession of the lease files, but rather access to them.
The amendments to the TRO further prohibited CMC from: (1) withdrawing any lease payments from certain accounts related to the Royal bonded lease pools; (2) removing any leases from Royal bonded lease pools without Royal’s consent; (3) depositing any Royal bonded lease payments into accounts other than those related to the Royal bonded lease pools; (4) instructing lessees in the Royal bonded lease pools to deposit or transfer lease payments into bank accounts other than those related to Royal; (5) depositing any proceeds from any collection activities related to any Royal bonded leases into bank accounts other than those related to Royal; (6) transferring any payments from leases that had been removed from the Royal bonded lease pools (“removed leases”) and placed into non-Royal accounts; and (7) selling or transferring any of the removed leases or any payments derived from the removed leases without Royal’s consent.
On February 26, 2002, the magistrate judge in the District Court Action entered an order requiring CMC to produce an electronic copy of all lease accounting data maintained by CMC with respect to the Royal bonded leases by March 4, 2002 (“February 26 order”). CMC also was required to produce or provide access to “the removed lease files bonded by the respective sureties” by March 6, 2002. On March 4, 2002, CMC provided compact discs containing lease accounting data and copies of some electronic files to counsel for Royal.
On March 8, 2002, counsel for CMC directed Royal and the other sureties by letter to retrieve their respective lease files from CMC’s offices on March 11, 2002. When James Patterson, counsel for Royal, arrived at CMC’s offices, the offices were vacated and closed. On the same day, by a faxed letter, counsel for CMC informed Royal and the other sureties that the lease files would be available for retrieval the next day. Mr. Patterson retrieved the lease files on March 12, 2002.9
On March 19, 2002, the district court approved a stipulation between CMC, Royal and the other sureties (“March 19 stipulation”) 10 whereby CMC resigned as sub-servicer. CMC also would make available for retrieval by Royal, beginning March 12, 2002, all of the original files related to its bonded leases. CMC was obligated to make all of the lease files available to Royal until it was able to inventory the *822files and verify that CMC indeed had made available all the necessary files. CMC further agreed to preserve and maintain and make reasonably available to Royal, for inspection and copying, all documents and records not previously made available to Royal, “however stored or maintained and wherever located, now in [CMC’s] possession or under [its] control related to the business or activities of CMC/CSC.”
B. Context of the Present Appeal
1. The prior appeal
On May 30, 2002, CMC filed a voluntary chapter 11 petition,11 which case later was converted to chapter 7 on July 12, 2002.12
More than a year after the petition date, the trustee commenced an adversary proceeding against NetBank.13 The trustee sought declaratory relief characterizing the transfers of the lease assets and transferred assets as secured loans, rather than true sales, and determining that NetBank did not perfect its interests therein. Assuming that NetBank perfected its security interest by taking possession of the lease assets and transferred assets pursuant to the March 19 stipulation, the trustee sought to avoid the transfers as preferential pursuant to § 547(b).14 With respect to any unperfected security interests in the lease assets or transferred assets, the trustee sought to avoid the transfers using his strong-arm powers pursuant to §§ 544 and 551.15
*823NetBank filed a motion for partial summary judgment, to which the trustee filed a cross-motion (collectively, “Partial Summary Judgment Motions”). In its motion for partial summary judgment, NetBank asserted that, contrary to the trustee’s argument, the transfers of the lease payments under the SSAs were true sales.
NetBank further contended that it held a perfected security interest in both the lease payments and the surety bonds. According to NetBank, the lease payments were payment intangibles within the meaning of Nevada Revised Statutes (“N.R.S.”) § 104.9102.16 Pursuant to N.R.S. § 104.9309, a security interest in a payment intangible automatically perfects upon sale.17 As its security interest in the lease payments was automatically perfected upon sale, NetBank argued, the trustee could not avoid it.
NetBank contended that the sale of the lease payments also perfected its security interest in the surety bonds. NetBank characterized the surety bonds as supporting obligations for the lease payments. Under N.R.S. § 104.9308(4), perfection of a security interest in subject collateral also perfects a security interest in the supporting obligation for the collateral. Because its security interest in the lease payments was automatically perfected upon sale, NetBank contended its security interest in the surety bonds also was perfected.
In his cross-motion, the trustee disagreed with NetBank’s characterization of the transfers as true sales, but agreed with NetBank’s characterization of the surety bonds as supporting obligations.
After a hearing on December 20, 2004, the bankruptcy court issued a memorandum decision in favor of the trustee. Analyzing the relevant statutes, official commentary and case law, the bankruptcy court found that the lease payments constituted chattel paper. As such, NetBank *824had to perfect its security interest in the lease payments by filing a financing statement, which NetBank did not do. The bankruptcy court did not expressly determine whether NetBank perfected its security interest in the surety bonds.
The bankruptcy court also went on to find that, upon examining the “four corners of the SSA,” the transfers were secured loans, rather than true sales.
On February 28, 2005, the bankruptcy court entered its order, granting the trustee’s cross-motion for partial summary judgment (“Partial Summary Judgment Order”) in its entirety. On May 20, 2005, the bankruptcy court entered final judgment as to certain claims for relief asserted by the trustee in his complaint.18 Net-Bank appealed the Partial Summary Judgment Order.
On appeal, in a published opinion, we affirmed in part and reversed in part.19 Commercial Money Center I, 350 B.R. at 469.
We agreed with the bankruptcy court that the transfers of the lease assets and the transferred assets under the SSAs constituted secured loans, not true sales, as they “[bore] far more hallmarks of a loan than a sale.” Id. at 483.
We disagreed with the bankruptcy court’s characterization of the lease pay-merits as chattel paper, however. Id. at 469. Although the leases themselves were chattel paper, id., based on- our analysis of applicable Nevada law,20 we determined that “[lease payments] stripped from the underlying leases are not records that evidence monetary obligations — they are monetary obligations.” Id. at 476 (emphasis in original). As such, the lease payments were payment intangibles.
We determined that genuine issues of material fact and legal issues still remained as to whether NetBank could perfect its security interest in the lease payments by possession of the leases through an agent and whether NetBank in fact had possession thereby. Id. at 487-88. We thus remanded to the bankruptcy court for further determinations. Id. at 488.
2. The present appeal
On September 6, 2006, the bankruptcy court issued a notice of a hearing regarding the remand (“Remand Hearing”), setting the hearing for November 17, 2006. Notice of Hearing on Remand re: Appeal # 2, docket # 177. Four days before the Remand Hearing, the trustee filed a motion for summary judgment as to the issues remanded to the bankruptcy court in the prior appeal (“Summary Judgment Motion”).21 NetBank opposed.
*825After the April 26, 2007 hearing on the Summary Judgment Motion, the bankruptcy court took the matter under submission. Thereafter, the bankruptcy court issued its memorandum decision, again in favor of the trustee.
The bankruptcy court first found that, as a matter of law, NetBank could perfect its security interest in the lease payments only by filing a financing statement. According to the bankruptcy court, N.R.S. § 104.9313(1) enumerated only certain kinds of property with respect to which a security interest can be perfected by possession; neither general intangibles nor payment intangibles were included.22
Even if NetBank could perfect its security interest by possession through Royal, the bankruptcy court continued, Royal itself did not take possession. Citing to Commercial Money Center I, 350 B.R. at 486, the bankruptcy court reasoned that NetBank, as the secured party, could not perfect its security interest in the lease payments by constructive possession where the debtor, CMC, had actual possession of the leases at all relevant times.
Examining the TRO and the amendments thereto, the bankruptcy court further determined that Royal did not have such possession of the leases as to provide sufficient notice that NetBank had a security interest in the lease payments. Moreover, the bankruptcy court found, the TRO and its amendments only provided Royal with access to the lease files; neither the TRO nor the amendments directed CMC to turn over the leases or otherwise grant Royal possession or control of the leases. The bankruptcy court noted that it was undisputed that Royal did not take actual possession of the leases until March 12, 2002, which fell within the 90-day preference period.23
For the first time, NetBank contended that some of the surety bonds were not supporting obligations, but instruments within the meaning of N.R.S. § 104.9102(l)(tt).24 Because NetBank had actual possession of those surety bonds outside the preference period, NetBank argued that it held a perfected security interest in them.
The bankruptcy court applied the law of the case doctrine to determine this issue. The bankruptcy court pointed out that, in its partial summary judgment motion, Net-Bank argued that the surety bonds were supporting obligations with respect to the lease payments. Consequently, NetBank argued its security interests in both the *826surety bonds and lease payments were automatically perfected on sale of the lease payments. In addition, in opposition to NetBank’s partial summary judgment motion and in his cross-motion for partial summary judgment, the trustee agreed that the bonds were supporting obligations. Accordingly, when the Partial Summary Judgment Motions were argued before the bankruptcy court, both parties were asserting that the bonds were supporting obligations. The bankruptcy court believed it implicitly determined that the surety bonds were supporting obligations by finding that NetBank did not perfect its security interest in the lease payments and that the trustee was entitled to summary judgment avoiding NetBank’s security interest in all of the transferred assets, including the surety bonds.
On July 2, 2007, the bankruptcy court entered an order granting the trustee’s motion for summary judgment in its entirety (“Summary Judgment Order”).25 Order Granting Trustee’s Motion for Summary Judgment, docket #204. The following day, it entered final judgment in favor of the trustee as to the claims for relief encompassed in his Summary Judgment Motion.
The FDIC appeals.26
II.JURISDICTION
The bankruptcy court had jurisdiction pursuant to 28 U.S.C. §§ 1334 and 157(b)(2)(B) and (F). We have jurisdiction pursuant to 28 U.S.C. § 158.
III.ISSUES
(1) Whether NetBank perfected its security interest in the lease payments.
(2) Whether the law of the case doctrine bars NetBank from arguing that the surety bonds are instruments, rather than supporting obligations.
(3) If not, whether the surety bonds are instruments.
IV.STANDARDS FOR REVIEW
We review de novo the bankruptcy court’s grant of summary judgment. Balint v. Carson City, 180 F.3d 1047, 1050 (9th Cir.1999). Viewing the evidence in the light most favorable to the non-moving party, we must determine whether any genuine issues of material fact exist, and whether the bankruptcy court correctly applied relevant substantive law. Id. We may neither “weigh the evidence [nor] determine the truth of the matter, but only determine!] whether there is a genuine issue for trial.” Id. at 1054. “We may affirm a grant of summary judgment on *827any ground supported by the record.” Simo v. Union of Needletrades, 322 F.3d 602, 610 (9th Cir.2003).
Summary judgment may be appropriate when a mixed question of fact and law involves undisputed underlying facts. Citicorp Real Estate, Inc. v. Smith, 155 F.3d 1097, 1103 (9th Cir.1998). Summary judgment is inappropriate, however, if any material factual issues exist for trial. Id.
We review conclusions of law and questions of statutory interpretation de novo. Abele v. Modern Fin. Plans Servs., Inc. (In re Cohen), 300 F.3d 1097, 1101 (9th Cir.2002).
We review the bankruptcy court’s application of the law of the case doctrine for an abuse of discretion. Milgard Tempering, Inc. v. Selas Corp. of America, 902 F.2d 703, 715 (9th Cir.1990).
Whether a writing is properly characterized as an instrument under the UCC is a question of law that we review de novo. See Omega Envtl., Inc. v. Valley Bank NA (In re Omega Envtl., Inc.), 219 F.3d 984, 986 n. 4 (9th Cir.2000) (per curiam).
Y. DISCUSSION
A. NetBank’s Security Interest in the Lease Payments
The FDIC contends that the bankruptcy court erred in granting summary judgment in favor of the trustee because a security interest in lease payments can be perfected by possession of the underlying leases, as reasoned in Gray v. Jefferson Loan & Inv. Bank (In re Commercial Management Serv., Inc.), 127 B.R. 296 (Bankr.D.Mass.1991) (“Commercial Management”).
Arguably, NetBank could have perfected its security interest either by filing a financing statement or by possession of the leases, as decided in Commercial Management. Based on the record before us, however, NetBank did neither.
1. No perfection by filing a financing statement
The filing of a financing statement is “by far the most common and important method” by which to perfect a security interest. White & Summers, Uniform Commercial Code, § 31-4 (5th ed.2002). It is undisputed, however, that NetBank did not file any financing statements with respect to the transferred assets or the lease assets; in its answer to the trustee’s complaint, Net-Bank conceded that it did not file any financing statements, and no financing statements were filed in its behalf, in either Nevada or California. NetBank thus did not perfect its security interest in either the transferred assets or the lease assets by filing.
2. No perfection by possession
Relying on the reasoning of Commercial Management, the FDIC argues that Net-Bank perfected its security interest in the lease payments by constructive possession of the leases through Royal, its third-party agent.
In Commercial Management, the bankruptcy court held that the assignee, Jefferson Loan and Investment Bank (“Jefferson”) perfected its security interest in lease payments by taking physical possession of the underlying leases, even though it did not file any financing statements as to the lease payments. 127 B.R. at 304.
The bankruptcy court in Commercial Management acknowledged that pre-revision UCC § 9-305 did not specifically provide that the transfer of chattel paper transferred the underlying obligation, nor did it specifically provide that perfection of a security interest in the chattel paper by *828possession perfected a security interest in the obligation. Id. at 302 (quoting Boss, Lease Chattel Paper: Unitary Treatment of a “Special” Kind of Commercial Specialty, 1983 Duke L.J. 69, 92 (1983)). The bankruptcy court believed, however, that possession of the chattel paper itself would be rendered meaningless unless the transfer of the chattel paper operated to transfer the rights embodied therein. Commercial Management, 127 B.R. at 302 (quoting Boss, 1983 Duke L.J. at 92-94).
We reviewed Commercial Management as part of our analysis in Commercial Money Center I. In light of certain provisions of the UCC and the reasoning of Commercial Management, we suggested that “a perfected interest in chattel paper [may] include[ ] the associated [lease payments],” possibly as proceeds. Commercial Money Center I, 350 B.R. at 479.
However, even if we determined that the holding of Commercial Management applied in the appeal before us, we conclude that NetBank did not effectually take possession of the leases through Royal for perfection purposes outside of the preference period.
a. Royal did not have actual possession of the leases
As one commentator has noted, “[possession is a notoriously plastic idea.” White & Sommers, Uniform Commercial Code, § 31-8(b) (5th ed.2002). Accordingly, the drafters of Article 9 of the UCC declined to define “possession.” Id. See also UCC § 9-313 cmt. 3 (2007).
The Nevada version of UCC § 9-313 also does not define “possession.”27 See N.R.S. § 104.9313 (2005). Under N.R.S. § 104.9313(3), a secured party takes actual possession of chattel paper through an agent possessing the collateral in its behalf.28 See N.R.S. § 104.9313(3) (2005); see also UCC § 9-313 cmt. 3 (2007). The commentary to UCC § 9-313 suggests that the agent cannot be the debtor, an agent of the debtor or any other person or entity “so closely connected to or controlled by the debtor that the debtor has retained effective possession....”29 UCC § 9-313 cmt. 3 (2007).
*829Within the Ninth Circuit, the agent must have actual possession of the collateral in order for the secured party to have a perfected security interest pursuant to UCC § 9-313. Heinicke, 543 F.2d at 701-02; Huffman v. Wikle (In re Staff Mortgage & Inv. Corp.), 550 F.2d 1228, 1230 (9th Cir.1977).30 See also Fogler v. Casa Grande Cotton Finance Co. (In re Allen), 134 B.R. 373, 376 n. 5 (9th Cir. BAP 1991). A secured party or its agent takes actual possession when the collateral is physically transferred to the secured party or its agent. Raiton v. G & R Props. (In re Raiton), 139 B.R. 931, 936 (9th Cir. BAP 1992) (defining “possession” under former Cal. Com.Code § 9-305). By having the agent take actual possession of the collateral, notice is provided to prospective third-party creditors that the debtor “ ‘no longer has unfettered use of [the secured party’s] collateral.’ ” Heinicke, 543 F.2d at 702 (quoting In re Copeland, 391 F.Supp. 134, 151 (D.Del.1975)); Huffman, 550 F.2d at 1230.
The leases were not physically transferred to Royal outside the preference period. According to the declarations of Mr. Patterson and William Hibberd, an actuary for Royal, Royal did not obtain physical possession of any of the original lease files until March 12, 2002. Given the uncontro-verted declarations of Mr. Patterson and Mr. Hibberd, the FDIC does not contest this point.
b. The TRO and the amendments did not give Royal control of the leases
The FDIC instead advances a two-pronged argument to establish that Net-Bank perfected its security interest in the lease payments by possession of the leases through Royal outside the preference period: (1) that Royal gained control over the leases through the TRO and the amendments thereto; and (2) that CMC held the leases in constructive trust for Royal.
The FDIC first argues that the TRO and its amendments provided Royal with sufficient control over the leases as to constitute possession. According to the FDIC, the TRO and the amendments “limited CMC’s control over the [l]eases to such a degree” as to notify third-parties that CMC no longer had “unqualified ‘possession’ ” of the leases and that Royal did. Appellant’s Reply Brief at 7.
As the bankruptcy court pointed out, however, neither the TRO nor the amendments to it provided Royal with control of the leases. The TRO and the amendments only required CMC and/or CSC to “make available” to Royal all the books, records and accounts related to the leases. The other provisions of the TRO and its amendments simply prohibited and re*830stricted CMC and/or CSC from removing the lease payments and the leases from Royal accounts and Royal bonded lease pools and from transferring the lease payments and leases to non-Royal entities and accounts. The TRO and its amendments did not by their terms enable Royal to exert or gain control over the leases, and thus provide the notice to third-party creditors that is the raison d’etre for perfection requirements under the UCC. In fact, Royal was not specifically authorized “to retrieve” the leases and lease files by order of the district court until the March 19 stipulation.
The record also shows that Royal had no intention of obtaining physical possession or control of the leases through the TRO and its amendments. As indicated by Mr. Patterson in his deposition testimony on December 7, 2006, Royal was not seeking possession of the lease files at the time it applied for the TRO. Rather, Royal’s objective “was to obtain access to this information.” In a letter to counsel for CMC, dated March 26, 2002, drafted by Mr. Patterson, Royal only sought access to the lease files so that it could “conduct a proper audit of the lease files.” The declaration of Mr. Hibberd in support of the TRO also demonstrates that Royal sought access to, not physical possession or control of, the leases.31
CMC was not required to make all of the lease files available to Royal for retrieval until CMC and Royal entered the March 19 stipulation. Unlike the March 19 stipulation, the TRO and its amendments did not mention retrieval. Notably, the March 19 stipulation made the date of Royal’s retrieval of the lease files retroactive to March 12, 2002.
Based on the record before us, we conclude that Royal did not gain such control over the leases through the TRO and its amendments as to constitute actual possession outside the preference period. Net-Bank therefore did not take constructive possession of the leases, at least during any period relevant for purposes of this appeal.
c. Royal did not have a constructive trust over the leases
The FDIC argues in the alternative that Royal had possession of the leases because CMC held the leases in constructive trust for Royal when the TRO and its amendments divested CMC of control over the leases.
We reject this argument. The FDIC, in effect, is using a back-door approach to establish perfection through possession by CMC. By arguing that CMC held the leases in constructive trust for Royal, the FDIC is attempting to characterize CMC as its agent indirectly.
As we explained in Commercial Money Center I, CMC cannot be the agent of NetBank for UCC Article 9 purposes, as a matter of law. Commercial Money Center I, 350 B.R. at 486-87. See also Huffman, 550 F.2d at 1230; Heinicke, 543 F.2d at 702. The debtor’s lack of possession and the creditor’s actual possession of collateral serve to notify third-party creditors that the debtor “no longer has unfettered use” of the collateral. Heinicke, 543 F.2d at 702. To conclude otherwise would defeat the notice function of perfection by possession under UCC § 9-313. See id.
*831Even assuming that CMC could be an agent for purposes of perfection by-possession, the FDIC cannot establish that a constructive trust should be imposed.
Property held in trust by the debtor for another generally is not property of the estate. Torres v. Eastlick (In re N. Am. Coin & Currency, Ltd.), 767 F.2d 1573, 1575 (9th Cir.), amended by 774 F.2d 1390 (9th Cir.1985). We look to state law to determine whether a trust will be imposed on property in a bankruptcy proceeding. Starr v. Bruce Farley Corp. (In re Bruce Farley Corp.), 612 F.2d 1197, 1200 (9th Cir.1980).
A constructive trust is a flexible, equitable remedy. Airwork Corp. v. Markair Express, Inc. (In re Markair, Inc.), 172 B.R. 638, 642 (9th Cir. BAP 1994). Although property may be subject to a constructive trust under state law, it is not automatically excluded from the bankruptcy estate. N. Am. Coin & Currency, Ltd., 767 F.2d at 1575. If there is no state court order imposing a constructive trust prepetition, then the right to such a remedy remains inchoate. See Elliott v. Frontier Props. (In re Lewis W. Shurtleff, Inc.), 778 F.2d 1416, 1419 (9th Cir.1985). We therefore act very cautiously in recognizing a constructive trust in favor of one creditor over another, as one of the strongest policies in bankruptcy law is equality of distributions among like situated creditors. N. Am. Coin & Currency, Ltd., 767 F.2d at 1575. Besides, “[b]ecause it is a remedy, a constructive trust cannot affect rights in the res until it is imposed.” Taylor Assocs. v. Diamant (In re Advent Mgmt. Corp.), 178 B.R. 480, 488 (9th Cir. BAP 1995) (emphasis in original). To date, no constructive trust has been imposed in favor of Royal or the FDIC on the leases.
In Nevada, a constructive trust arises when the holder of property is determined to be a trustee of that property for the benefit of another who in good conscience is entitled to it. Locken v. Locken, 98 Nev. 369, 650 P.2d 803, 804-05 (1982) (per curiam). Courts may impose a constructive trust where: (1) there is a confidential relationship between the parties; (2) it would be inequitable to allow the holder to retain the property; and (3) it is essential to the effectuation of justice to impose such a trust. Id. at 805. The party requesting the imposition of a constructive trust must prove these circumstances by clear and convincing evidence. Randono v. Turk, 86 Nev. 123, 466 P.2d 218, 222 (1970).
The FDIC claims that all of the circumstances for imposition of a constructive trust exist. We disagree.
With respect to the first factor, the FDIC has not shown by clear and convincing evidence that a confidential relationship existed between CMC and Royal. Under Nevada law, “[t]he essence of a ... confidential relationship is that the parties do not deal on equal terms.” Giles v. GMAC, 494 F.3d 865, 881 (9th Cir.2007) (quoting Hoopes v. Hammargren, 102 Nev. 425, 725 P.2d 238, 242 (1986)) (internal quotation marks omitted). By virtue of the trust and confidence placed in and accepted by one party, that party is in such a superior position as to exert a “unique influence” over the dependent party. Giles, 494 F.3d at 881. A confidential relationship exists where “ ‘one party gains the confidence of the other and purports to act or advise with the other’s interests in mind.’ ” Id. (quoting Perry v. Jordan, 111 Nev. 943, 900 P.2d 335, 338 (1995) (per curiam)).
The FDIC asserts that CMC had a confidential relationship with Royal because CMC was sub-servicer, as provided for in the SSAs. Nothing in the record indicates, however, that Royal had placed such trust *832and confidence in CMC as to enable CMC to exert a “unique influence” over Royal. Under the SSAs, CMC was no more than an agent for Royal. CMC merely performed Royal’s servicer duties by collecting the lease payments and distributing them to the third-party investors.
With respect to the second and third factors, we cannot agree with the FDIC that CMC’s conduct, in light of the effects of the TRO and its amendments, was so inequitable as to require the imposition of a constructive trust. Clear and convincing evidence in the record does not mandate a constructive trust remedy.
Moreover, as we pointed out in Commercial Money Center 7, NetBank was a sophisticated commercial entity that should have acted further to protect its security interests. Id. at 486. The FDIC has not shown that NetBank was prevented from verifying whether CMC filed financing statements or from taking possession of the leases itself. It is inappropriate to impose a constructive trust where a commercially sophisticated creditor did not take reasonable steps to ensure that its security interests were perfected.
Based on the record before us, we conclude that the bankruptcy court did not err in finding that NetBank did not perfect its security interest in the lease payments by filing a financing statement or by taking possession of the leases through Royal. Because the FDIC failed to raise a genuine issue of material fact to support a finding of perfection of its security interest in the lease payments, outside of the preference period, the bankruptcy court properly granted summary judgment to the trustee avoiding the claimed security interest.
B. NetBank’s Security Interest in the Surety Bonds
The FDIC asserts that the bankruptcy court erred in granting summary judgment for the trustee because a genuine issue of material fact exists regarding the characterization of surety bonds as purely supporting obligations, or as instruments under the UCC.
The FDIC argues that the bankruptcy court applied the law of the case doctrine too broadly when it declined to consider the issue. The law of the case doctrine, the FDIC contends, only precludes the lower court from reconsidering issues decided either explicitly or by necessary implication by the higher court. No explicit or implicit finding was made in the prior appeal as to whether the surety bonds constituted instruments or supporting obligations. To the extent that the bankruptcy court implicitly determined that the surety bonds were supporting obligations, the FDIC adds, our partial reversal and remand in the prior appeal effectively “unmade” that determination. The bankruptcy court thus was free, the FDIC concludes, to address the issue on remand.
We believe that the law of the case doctrine does not apply to the issue. Under the law of the ease doctrine, a court is barred from reconsidering an issue that already has been decided in the same court or in a higher court in the same case. Milgard Tempering, Inc. v. Selas Corp. of America, 902 F.2d 70S, 715 (9th Cir.1990). For the law of the case doctrine to apply, the issue must have been decided, either expressly or by necessary implication. Id. However, even if the law of the case doctrine applies, a court may decide, in its discretion, to revisit the issue if: “(1) the first decision was clearly erroneous and would result in manifest injustice; (2) an intervening change in the law has oc*833curred; or (3) the evidence on remand [is] substantially different.” Id.
We did not make any determination as to this issue in the prior appeal. Our determinations were limited to the issues of whether the transfers under the SSAs constituted sales or secured loans and whether the lease payments constituted payment intangibles.
As to the bankruptcy court, it neither expressly nor implicitly decided whether the surety bonds were instruments or supporting obligations in its memorandum decision on the Partial Summary Judgment Motions. The bankruptcy court simply assumed that the surety bonds were supporting obligations because both NetBank and the trustee argued that the surety bonds were supporting obligations and determined that NetBank did not have a perfected security interest in the lease payments.
C. The Surety Bonds Are Supporting Obligations and Not Instruments
The FDIC contends that a triable issue of material fact remains as to whether at least some of the surety bonds are instruments rather than purely supporting obligations. We disagree.
The FDIC argued that even if the surety bonds are supporting obligations, that characterization is not necessarily exclusive, and the surety bonds could be instruments as well. At oral argument, counsel for the trustee conceded that at least theoretically, collateral for a loan could be both a supporting obligation and an instrument, but denied that the surety bonds in this case could appropriately be characterized as instruments.
“The question of whether a particular document qualifies as an instrument under the U.C.C. is a question of law.” Coral Petroleum, Inc. v. Banque Paribas (In re Coral Petroleum), 50 B.R. 830, 837 (Bankr.S.D.Tex.1985). See also Omega Envtl., Inc., 219 F.3d at 986 & n. 4 (determining whether a certificate of deposit is an instrument within the meaning of Va.Code § 8.9-105(1)(i)).
N.R.S. § 104.9102(1)(xxx) defines a “supporting obligation” as a letter-of-credit right or secondary obligation that supports the payment or performance of a general intangible. N.R.S. § 104.9102(1)(tt) defines an “instrument” for UCC Article 9 purposes (it is defined differently in UCC Article 3), as:
a negotiable instrument or any other writing that evidences a right to the payment of a monetary obligation, is not itself a security agreement or lease, and is of a type that in ordinary course of business is transferred by delivery with any necessary endorsement or assignment.
By their terms, the surety bonds are assignable.32 In fact, CMC purported to transfer all rights under the surety bonds to NetBank under Article II, § 2.1(a)(iii) of the SSAs. However, the surety bonds are not transferred by delivery in the ordinary course of any party’s business independent of the underlying equipment leases and lease payments. In fact, at oral argument, counsel for both *834parties confirmed that there is no “market” for the surety bonds.
In determining whether particular written documents are “instruments,” “most courts defer to the realities of the marketplace rather than narrowly looking to the form of the writing.” McFarland v. Brier, 850 A.2d 965, 975 (R.I.2004) (quoting In re Omega Envt'l, Inc., 219 F.3d at 987) (internal quotation marks omitted). In this case, the reality is that the surety bonds have no meaningful existence independent of the equipment leases they support for security purposes. Indeed, numbered section 1 of the surety bonds provides that “[i]f all payments required by the Lease are made in accordance with the Lease provisions, then this obligation shall be void.... ”
Accordingly, the surety bonds do not represent absolute rights “to the payment of a monetary obligation.” They do not provide for the payment of any sum certain. Rather, payments under the surety bonds are contingent on the existence of payment default(s) under the particular equipment leases to which they relate.33 As stated in numbered section 2 of the surety bonds, “[t]his Lease Bond and the Surety’s obligation constitute an unconditional and absolute guarantee of payment, not collection.”
The surety bonds list CMC (and its successors and assigns) as the obligee and Royal as the surety. Reviewing a copy of a surety bond issued by Royal, we note that the surety bond was issued for Royal to underwrite the leases and to remedy any default in the lease payments. Specifically, the surety bond states in its preamble that Royal, as surety, “agrees to pay to the Obligee any amounts due and owing by the principal with regards to the lease.” The surety bond further states that Royal “is responsible to Obligee for the individual underwriting of each lessee and Lease, including, but not limited to ... the accurate and timely performance by any sub-servicer designated by [Royal].” The record does not include any surety bonds with varying language.
An audit letter dated January 8, 2001 from Laura Moon, chief accounting officer for NetBank, to Charles Deyo, senior vice-president underwriting facility manager of Royal, further indicates that the surety bonds constitute supporting obligations, rather than instruments. Per the January 8, 2001 letter, Ms. Moon asked that Mr. Deyo confirm that the surety bonds guarantee payment by Royal to NetBank of all lease payments and any defaults thereon.34 *835The January 8, 2001 letter included a document titled, “Request for Confirmation” (“confirmation form”). The confirmation form asked that Royal verify whether the information regarding each surety bond was correct. At the October 8, 2003 deposition of Ms. Moon, she testified that she understood the purpose of the January 8, 2001 letter was “to confirm the arrangement [she] believed was in place with Royal.” At a deposition on August 20, 2003, Mr. Deyo testified that he verified the surety bonds in question and signed the confirmation form.
By their terms, the surety bonds fundamentally are not instruments. They are supporting obligations provided for security purposes. The surety bonds guarantee lease payments up to a maximum amount in the event of default, but they do not stand independent of the underlying leases as monetary payment obligations. The surety bonds are not bought, sold, transferred or assigned as such. Based on the record before us, it appears that NetBank and Royal themselves understood and characterized the surety bonds as supporting obligations. As NetBank did not perfect its security interest in the lease payments, it did not perfect its security interest by possession of the supporting obligation surety bonds. Although the bankruptcy court did not make its decision on these grounds, there was no error in granting summary judgment in favor of the trustee avoiding NetBank’s security interest in the surety bonds.35
VI. CONCLUSION
Based on the record before us, NetBank did not properly perfect its security interest in either the lease payments or the surety bonds outside the preference period. The bankruptcy court did not err in granting summary judgment in favor of the trustee avoiding NetBank’s security interest in the lease payments and the surety bonds. Therefore, we AFFIRM.