Invite people to your warehouse and tell them there’s cake with special ingredients. Hide the cakes in the vault room and destroy the vault keys and leave lots of bread in the accessible part of the warehouse.
Open the doors.
They will come in in swarms. Once the bread has all been snatched… they will enquire about the cakes (coz they’re greedy). Tell them the cakes are in the vault but you have destroyed the keys.
Grab your popcorn and see who does what.