Here is the opinion in Wells Fargo Bank NA v. Cabazon Band of Mission Indians.
The indenture and note between the Bank and the Tribe were secured by a perfected security interest in the DAR, after being deposited into the Tribe’s custodial account with the Bank. The indenture agreement at issue here did not confer any authority, control, or responsibility to the bondholder or the Bank for the conduct of any gaming activity. It merely provided the Bank and the bondholder with a security interest in a specific bank account. It did not and could not control what was deposited into that custodial account. A contract creating a security interest in a custodial account does not convey authority or responsibility for the conduct of any gaming activity. Therefore, it does not violate the sole proprietary interest rule.
Only brief I’ve found: Wells Fargo’s Reply brief