Darr was last seen on the evening of May 27, 2008. when he left his home in the Village of Clover Ridge retirement community near Sand Dune Road and Logan's Ferry Road in Murrysville, Pennsylvania. He was going for a walk. There was a heavily wooded nature area nearby, and Darr frequently walked its trails. He never returned home and has never been heard from again. His wife reported him missing at 10:00 a.m. the next day.

An extensive search of the area turned up no sign of Darr. He was in fairly good physical and mental health at the time of his disappearance. He has no history of leaving without warning and he wasn't having any personal problems in 2008, but he did suffer occasional memory lapses. Darr did not use a cellular phone or credit cards at the time of his disappearance, and he hasn't renewed his prescriptions or accessed his bank accounts. Foul play is not suspected in his case, which remains unsolved.