The University of Texas at Austin is missing about 100 brains.

That’s about half of the specimens the university had in a collection of brains preserved in jars of formaldehyde. One of the missing brains preserved is believed to have belonged to clock tower sniper Charles Whitman.

The co-curator of the collection is psychology Professor Lawrence Cormack. He tells the Austin American-Statesman that undergraduates and others may have been swiping the brains for years “for living rooms or Halloween pranks.”

The Austin State Hospital had transferred the jars of brains to the university about 28 years ago.