This is one of those cases where it's impossible to determine who did what. The screenshots only show the black mask being sold in the GE, before that we can see the supplies were bought for fight caves. In the bank there are no placeholders or any other factor that hints to the items being there in the first place. Even if there were it would still be impossible for us to tell who actually took the items since 3 people were able to access the account at the time. I'm sorry but unfortunately you will have to take the loss on this one.