D’Quan Young, 24, with Jordan, his 4-year-old daughter. (Family photo)

A man armed with a gun and an off-duty D.C. police officer fired “almost simultaneously” during a brief confrontation that ended with the man dead, police said Tuesday, offering the most detailed account yet of the encounter last week.

D.C. Police Chief Peter Newsham said the May 9 incident began as the officer, dressed in plainclothes, was headed to a cookout in a neighborhood he did not know well around the Brentwood Recreation Center in Northeast Washington.

Newsham said D’Quan Young, 24, crossed the street and approached the officer as he talked on his cellphone. The chief said Young “confronted the officer about why he was in the neighborhood” and moments later there was “an exchange of gunfire.” Young was struck and died at a hospital. The officer was not injured.

Newsham said he believes the officer saw Young with a gun in his hand and perceived a threat but said it was unclear who fired first. He said it also is unclear whether Young knew the other man was a police officer. The chief said he did not think the officer had time to identify himself.

The new information comes after the officer provided a statement to detectives investigating the shooting, which occurred about 6:50 p.m. in the 2300 block of 15th Street NE, in the Montana Terrace apartment complex. Newsham also said investigators had obtained surveillance video, though it shows only part of the confrontation and was taken a long distance away. Police also said they have found a gun at the scene and have forensic evidence showing Young and the officer both fired weapons. The officer’s lawyer did not respond to an interview request.

The shooting raised questions last week as police discussed a chaotic aftermath in which many officers rushed to the sound of gunshots. A sergeant pulled the officer who fired away from the scene, apparently fearing for his safety amid an angry crowd, and failed to immediately notify superiors that a police officer had fired his weapon, police said. That sergeant has been suspended pending an internal investigation.

Young’s family has been critical of the police response and the shooting and questioned whether Young had fired a gun. On Tuesday, Young’s grandmother Phyliss Young, 53, said she has not heard the latest details given by police. She said she doesn’t believe what they say. “I think they’re covering up,” Young said. She declined to comment further.

Mayor Muriel E. Bowser (D), interviewed on Monday before the new details were revealed, said she is focused on “finding out what happened” but cautioned that not all the facts are known.

The mayor declined to make public the name of the officer who fired, as she did after an officer fatally shot a motorcyclist in 2016 and had failed to turn on his body-worn camera. That case, she said then, warranted an exception to the department’s policy about withholding the identities of officers involved in shootings because of the serious questions raised about the incident.

In this case, Bowser said, “Like we’ve done in other difficult circumstances, we have been open and transparent with the community. When it’s appropriate, we show what we know.”

Newsham’s comments this week are more forceful than those provided during a Friday update on the incident. At that time, the officer had not yet spoken with investigators and Newsham had few new details to discuss.

On Monday, the chief for the first time discussed Young’s criminal record, noting two previous arrests involving guns. One resulted in a conviction. “One of the things that is most disturbing to me,” Newsham said, “is why we had a man that close to one of our rec centers . . . carrying a gun and confronting people. What would have happened if he had confronted one of our unarmed kids?”