How do I deal with a friend stealing money from another friend?

I caught him! I tend to mind my business but I dead saw my friend take money that did not belong to him and it wasn’t an accident.

Here’s the scenario… At a friends house drinking and just playing poker. We order food, all chip in and pay the delivery guy. My drunk friend threw in a $50 cause it’s all she had (expecting change even in her drunken state). So we pay for the pizza and her change sits on a counter for awhile. It’s then that I see a mutual friend pocket a $20. I know he’s down and out..but still!? Do I cause a crazy amount of trouble or just mind my business? I should add that the thief is very close to my friend and I’m not even sure that she would believe me over him.

I must stress that this was definitely shady, he did NOT take the money by accident. I don’t even think he threw in money for the food.