D.C. police Chief Peter Newsham said at a news conference that the victim was pronounced dead at the scene.
A police spokesman said Johnson was found on the front steps of an apartment building. Newsham said he had been shot multiple times and that it appears he was targeted. He said the motive for the killing is not yet known.
“It appears they were looking for this young man in particular,” Newsham said.
The chief complained about the proliferation of illegal firearms and said consequences for people involved in violence need to be harsher. “We need to let young people know that carrying a firearm is not pretty, it is not cute,” he said. “And people end up dead as a result.”
Police said the shooting did not appear to be related to the fatal shooting in September of Marquette Harris, 27, who was attacked about three blocks away in the 200 block of P Street SW. No arrest has been made in that case.
The Nationals play the Los Angeles Dodgers in California on Wednesday night, but the ballpark invited fans to watch the game on its large television screens. Newsham said the shooting and investigation would not affect those plans.
Clarence Williams contributed to this report.