This is a story relayed by a colleague in a different university department, and is sort of the opposite of embezzling.
My friend and a helper were cleaning out an old storeroom in the basement. They came across a zipper money bag full of cash. My friend immediately sent the student helping to go get the department chair and accountant. Now with witnesses present, they counted out several thousand in cash. They also discovered thousands in 20 year old uncashed checks made out to the department.
The checks were enough of a clue to work out what had happened. At some point, 20 or so years ago, the department had hosted a conference. Attendees paid by check or cash (this would have been in the 90s), but making deposits was a pain, so the former accountant had just put everything in the back of a file cabinet, and forgot about it.