Matt Lambert, a 55-year-old doctor, then fatally shot himself while holed up in his apartment, where he had been speaking by phone with police negotiators, said Jeffery Carroll, interim chief with the Metropolitan Police Department.
Lambert was locked in rancorous litigation with management over mold and moisture problems in his seventh-floor unit, court records show.
Mayor Muriel Bowser said she was "devastated" at the loss of life in a "senseless act of gun violence."
The shootings occurred around 8 a.m. in Logan Circle, about a mile (1.6 kilometers) north of the White House. Much of the block on 15th Street Northwest was cordoned off as police urged people to avoid the area, which includes a VIDA Fitness center, St. Luke's Episcopal Church, residences and a Whole Foods store. Schools were locked down.
Law enforcement SWAT teams and other officers had their guns drawn on the roof of a building and on the ground below. Carroll said Lambert, armed with three guns, shot and wounded four people from his condo patio. Three sustained non-life-threatening injuries and the fourth remained in critical condition by late afternoon.
"This whole incident took place in less than five minutes. ... I can only imagine being in that area and hearing the gunshots or being inside the gym," he said.
The man killed at VIDA gym on the ground floor was identified as James Stuart, 46, the building manager, the police chief said.
"There has been an ongoing dispute between the suspect in this case" and management "regarding maintenance issues, mold and the like. We believe it's related to that," Carroll said.
Lambert had filed a lawsuit, alleging that he hadn't been able to enjoy his penthouse since 2024 because of mold, moisture and water problems, records show. He claimed the problems began after a contractor had worked on the building's exterior.
The litigation was ongoing, according to court filings. Lambert appeared to share his condo woes, including photos and an engineering report, on an X site titled OfMiceandMold. The report was described online as "my manifesto."
Speaking to reporters, Lambert's lawyer, Joel Braithwaite, said he was "deeply shaken and saddened" by the violence. He said the condo resembled a "war zone" because of its conditions and said Lambert had spent more than $300,000 in pressing the lawsuit.
"I don't think there's any sense to be made," Braithwaite said of the shootings. "I can't give you that closure."
Braithwaite said Lambert had lived in the unit since 2017. Online property records show he bought it in September 2016 for nearly $1.1 million.
James Spellman, who was at the gym, said there were about 50 people there when the shootings began.
"Within seconds there was a man who fell to the ground, and a pool of blood came out," he said. "One gym member rushed to help him. He was instantly dead. He had been shot in the neck."
Anthony Mirones was in the gym's cardio area when he heard a loud bang and thought something fell off the wall. He said someone was trying to help the wounded man but then a fire alarm went off and many people ran.
"The people in cardio had to step over the body," Mirones said.
Another witness, Ryan Dubicki, said he was in his nearby apartment around the same time when he "heard about five bangs."
"They were really spread out so I thought it was construction," said Dubicki, an AP employee on the elections team. A short time later "there were cops everywhere."
While inside his condo, Lambert also cut a natural gas line to the fireplace and started a fire, triggering the sprinkler system, which quickly contained the flames, Carroll said.
The Washington Sun posted an online story by Michael Brice-Saddler, who said he had interviewed Lambert last year about his condo problems. Lambert had told another resident that he knew Stuart's morning routine at the VIDA gym.
"If you want to see the building manager," Brice-Saddler quoted Lambert as saying, "he comes in the gym about 8 o'clock."