Mark David Zeichner was 34 when he was last seen on June 15, 1984, in his Queens, New York, apartment. He was living alone and left behind clothing, personal items, his wallet and identification, details that have raised concern about the abruptness of his disappearance.

Zeichner had diagnoses of bipolar disorder and schizophrenia, a history of resisting medication, past drug use and a prior suicide attempt. There have been no confirmed sightings or substantive leads since he vanished. Speculation that he might have become homeless has not been supported by concrete evidence, and investigators have been unable to develop further details.

Anyone who knew Mark, saw him around June 15, 1984, or has information about his whereabouts is asked to contact local authorities. What information might help move this cold missing-person case forward?