A Navy medic shot and wounded two US sailors at a military facility today, then fled to a nearby Army base where security forces shot and killed him.
Authorities said they had yet to determine what drove 38-year-old Fantahun Girma Woldesenbet to open fire at the facility, located in an office park in Frederick, Maryland.
"We're still trying to sort through stacks of paper ... to figure out exactly what the motive would be," said Frederick Police Lieutenant Andrew Alcorn.
Woldesenbet shot the sailors with a rifle inside the facility at the Riverside Tech Park on Tuesday morning (Wednesday NZT), causing people inside to flee, said Frederick Police Chief Jason Lando.
Woldesenbet, a Navy medic assigned to Fort Detrick but who lived in town, then drove to the base, where gate guards who had been given advance notice told him to pull over for a search, said Brigadier General Michael J. Talley.
But Woldesenbet immediately sped off, making it about a half-mile into the installation before he was stopped at a parking lot by the base's police force. When he pulled out a weapon, the police shot and killed him, Talley said.
The two sailors, who Talley said were assigned to Fort Detrick, were airlifted to a hospital. Police said one victim is in critical but stable condition, and the other is in serious condition but expected to be released tomorrow.
Talley said investigators will determine as much as they can, including why the suspect went back to the base.
"[I] don't know his mental status at the time, and we're certainly going to find all that out," he said.
The brigadier general said the facility where the shooting took place was not under his command. He declined to identify the facility more specifically or describe the work that was done there.
Fort Detrick is home to the military's flagship biological defence laboratory and several federal civilian biodefence labs. About 10,000 military personnel and civilians work on the base, which encompasses about 1300 acres in the city of Frederick.
The base is a huge economic driver in the region, drawing scientists, military personnel and their families.
Police cordoned off Woldesenbet's apartment building in Frederick City, a few miles from the site of the shooting.
A neighbour, Ava Target, said she knew Woldesenbet only by sight, and that he lived on the top floor of the apartment complex with his wife and two kids. She wasn't aware of any problems.
Lando called the shootings "very tragic".
"It's happening too frequently," he said. "Every time we turn on the TV we're seeing something like this happening. And now it's happening in our backyards."