Tammen was last seen on April 19, 1953, in Old Fisher Hall, a former Victorian mental asylum that had been converted into a dormitory at Miami University in Oxford, Ohio. He was a resident hall advisor at Fisher Hall, and lived in room 225. At 8:00 p.m., he requested new bedsheets because someone had put a dead fish in his bed. Sometime around 8:30 p.m., Tammen apparently heard something outside his room that disturbed him, and went out into the hallway to investigate. He never returned. There is no indication that Tammen left on his own accord. His belongings were left behind in his dormitory room, and he also left the lights on and the radio playing. His gold 1938 Chevrolet sedan was not taken from its place in the school parking lot. Five months before he vanished, he went to the Butler County Coroner's office in Hamilton, Ohio and asked for a test to have his blood typed. The coroner claims that this was the only such request he ever got in 35 years of practice. It's unknown why Tammen wanted the test done. His disappearance remains unsolved.