Are you the creditor or the bankrupt person?
What was the credit for.
and when you say, you were asked to money back, and bakruptsyc creditro trust do you really mean that you were asked to give money back to the bankrupt person by the trustee of the bankrupsy estate?
In this case, you would claim this loss on form Schedule D.
this assumes that this is not a settlement due to a judgment for your non-performance.
If this was a settlement as part of the bankruptsy and you lost money on your investment to the fiancial institution, you woudl use schedule D.