The elderly man’s neighbors would see him from time to time on Quincy Street NW, getting fresh air, sometimes in a wheelchair. He had lived in the same house for about 30 years, residents said, with a steady stream of relatives coming and going.

Shortly before 6 a.m. Tuesday, a dispute inside the two-story rowhouse in the Petworth neighborhood led to tragedy. Police said a 55-year-old man shot his 79-year-old stepfather behind his ear.

The stepson then walked out the back door of the house and shot himself in the head, D.C. police spokesman Araz Alali said.

The 79-year-old man was in critical condition at a hospital, according to authorities. The stepson, identified as Bryan Wayne Russell, was pronounced dead at the scene. Police said officers recovered a revolver in the back yard, three blocks from the Georgia Avenue-Petworth Metro station.

By mid-morning, with the 500 block of Quincy Street still blocked off by police, neighbors began emerging to see what was happening. Several knew the wounded man by sight but not his full name, and they said two sons lived with him.

“He was the nicest guy in the world,” said Derrick Collins, who lives on the block. Another resident, Shirley White, said: “He didn’t hurt anybody.” Both said they knew that the man was sick and saw him using a wheelchair but didn’t know any details.

Detectives were trying to determine a motive. In earlier descriptions of the crime, police, citing relatives, misidentified the apparent shooter as the elderly man’s son and then grandson before settling on the stepson. Police also gave incorrect ages in initial accounts.

A relative reached by phone Tuesday said she did not want to speak publicly about what had happened. Of the shooting victim, she said, “He’s doing okay.”