If you have internet access at work, invest in a Blink security camera. You can set it up to view the footage over your cell phone. No fees or contracts....just the initial purchase and a set of aa batteries. You can use it at home afterward for your home security.
Encountered this situation once. A creative person in the office made peanut brittle with a healthy dose of habenero sauce. The offender took the bait. Claimed to have sucked off his own nipple in search of milk. The problem was resolved.
Years ago we had a girl that would help herself to anything without asking.. One day a Chinese guy asked me if I could get him some wild black walnuts.. Next day I brought him in a box full and left them out in full view... Next day girl comes in and her hands are yellow....
Careful with cameras in the workplace unless you HR is on board. The best is something really really hot. Laxatives are hard to play off as not intentional. Some ghost pepper powder hidden in the middle of something is easier because you can just say you like spicy food.
I wish there was a way to rig a Tupperware full of brownies with exploding blue dye like the banks to with money - or a product you could put in a brownie that would turn someone's teeth black when they bit it....I like the idea of hot powder though, that's a good one.
Careful cooking with those powders...turned my house into a gas chamber one day. Frying potatoes I thought “damn, that reaper powder I use on pizza would be good in this”, didn’t work out well. The house emptied as we all went looking for fresh air. Had to open all the windows and everything.