The answer finally arrived this year, too late for Ms. Davis. She had died four years earlier, still convinced Kevin would return to his childhood home. She was so certain, she had refused to have him declared dead for legal reasons, even though it would have facilitated the sale of a home in his name.

Mr. Germany, who was born in 1952, was a promising student; he once participated on “Scholastic Quiz,” a television game show in Washington, D.C. — his appearance memorialized in a newspaper clipping that his mother had saved. In 1974, he joined the Army, only to be honorably discharged a month later for medical reasons; Ms. Zwana said she was not told the specifics.

He returned to New York and enrolled in Queens College, earning a technical degree.

“Then he started having more mental health issues,” Ms. Zwana said. Paranoia, talking to himself, extreme weight gain and loss — doctors diagnosed him with schizophrenia, and he was in and out of hospitals.

In April 1990, Mr. Germany was admitted to Elmhurst Hospital Center, and was later transferred to Mount Sinai Hospital. His condition was severe enough that he was placed in a locked psychiatric unit, and his sister said he was taking three medications for anxiety and bipolar disorder.

A month later, the hospital called his family. Mr. Germany had disappeared. He had been assigned to a locked wing, but he had somehow walked away.