The shooting happened about 7 p.m. at 10th and P streets NW, Contee said.
“There was a dispute in the block between one victim and the suspect,” he said. “The suspect produced a handgun” and fired, striking the victims, he said. Two other members of the family, one of them a child, were present when the shooting happened, he said.
Police thought that the argument was about where a scooter was parked, Contee said.
Those shot were members of “an innocent family,” the chief told the news media in a briefing Tuesday night near the scene.
“Senseless gun violence in our city is totally unacceptable,” he said.
“We’re devastated,” said D.C. Mayor Muriel E. Bowser (D), who attended the briefing. “We have to say to the community, ‘we’re going to stand against gun violence.’ ”
An initial account said the assailant fled on a bicycle. However, Contee said he fled on foot, heading north. As of late Tuesday, no arrest had been reported.
The mainly residential area is east of Logan Circle and south of Rhode Island Avenue NW and the Shaw playground.
“It’s horrific,” said Rachelle Nigro, an advisory neighborhood commissioner who represents the area, calling it “a continuation of crime in our neighborhood that the city needs to get a hold of.”