A thief struck the University Gallery in June of 1967, stealing 6 prints right out of their frames. According to the theft report in the files, the prints (meaning woodcuts, lithographs, and the like) were works by very well-known artists, including Pablo Picasso, Henri Matisse, Max Beckmann, and Ernst Ludwig Kirchner. The report states:

The group of 13 prints was installed at the request of the Art History Department as a Study Exhibition for Art I Classes, and was to be retained until the end of the examination period for Spring Quarter, June 9. The prints were scheduled to be taken down this morning, June 12. The 6 missing prints were the more valuable ones of the entire group of 13... Their disappearance was discovered by Mr. Larry Gruenwald, Technician at the Gallery, upon his arrival at the Gallery, Monday June 12, at 7:30 a.m.

The file includes letters to auction houses alerting them to the theft, in case the stolen prints should come up for sale. I couldn't find any evidence that the prints were ever returned however... I guess this remains an unsolved mystery.