The thief had to walk past a security desk in the lobby, take the elevator up to our floor, walk past a front desk to the kitchen, then open a door to get to the office area. Probably sounded like enough layers for whoever was in charge of security at the time, but both desks were frequently unoccupied during lunch.
I know we had cameras too, but I never got updates on the investigation. I suspect it was an employee at one of the other companies in our building.