A brazen art thief recently stole Cartel de Don Juan Tenorio by Salvador Dali, valued at over $150k, from the Venus Over Manhattan Gallery in New York by distracting the guard and walking out with the piece in broad daylight. Then he sent it back.
The gallery put the word out about the thief, but didn't expect to get the work back, until they received an anonymous email saying it had been sent back, and it was delivered to the gallery later that week via Express Mail.
Why would someone do such a thing? Your guess is as good as mine...