Unable to undo secure safe/briefcase access panels

[nopiz]

After trying again, you are right about the mastermind thing. I had heard it had something to do with a multitool and the access panel but clearly not, you just need to slap in the code and read the message it gives you.
That said, the message doesn't appear if you are attempting to input the code while the briefcase is in your hand - you still need to drop it and work it out from there