WASHINGTON (REUTERS, WASHINGTON POST) - A 26-year-old woman armed with a handgun opened fire on Thursday (Sept 20) at a Maryland distribution centre for the Rite Aid drugstore chain, killing three people and wounding three others before taking her own life, the Harford County sheriff said.
The shooting unfolded shortly after the suspect, a temporary employee there, reported for work at around 9am EDT (9pm Singapore time) at the warehouse in Perryman, Maryland, about 55km north-east of Baltimore, Sheriff Jeffrey Gahler said at a news conference.
The sheriff's office identified the assailant in a tweet as Ms Snochia Moseley from Baltimore County.
The sheriff said investigators have not yet determined a motive, but a law enforcement source told Reuters the shooting was believed to have been sparked by a work-related grievance.
The fact that the assailant was a woman was unusual, given that the overwhelming majority of mass shootings in the United States are committed by men.
Sheriff Gahler said Thursday's gun violence began outside the warehouse and then moved inside, but investigators were still piecing together the precise sequence of events.
He said a total of seven people were hit by gunfire and that four, including the woman who opened fire, were killed. The three others were expected to survive, according to the sheriff. He said the suspect shot herself in the head.
No shots were fired by any law enforcement officer, he said.
The Rite Aid centre, located among other warehouses in an industrial park, has nearly 1,000 employees, company spokesman Pete Strella said.
The facility packages pharmaceuticals and other products for delivery to more than 2,500 stores.
Police spent several hours searching the 210,000 sq ft building for any possible additional victims, the sheriff's office said.
"Our prayers are with all those impacted, including our first responders," Governor Larry Hogan wrote on Twitter. "The State stands ready to offer any support."
Agents from the Baltimore offices of the federal Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) and the FBI also responded, the agencies said.
The shooting occurred a day after a man shot and wounded four people, including a police officer, at a Pennsylvania court building before he was killed by police, according to Pennsylvania State Police.
A man who said he was two blocks from the area told WBAL-TV that dozens of police officers arrived, jumped out of their cars and began to run.
Workers at a nearby auto repair shop said they locked their doors, said the Washington Post.
There are several businesses in the area that are housed in warehouses.
One woman told WBAL that her mother works at a building in the area and she became worried after not immediately hearing from her. As she was on the phone with the TV station, she got a text from her mother indicating that she was okay.
The incident comes after three people were killed and two others wounded in a shooting at a business park in October 2017, said the Post. And in 2016, two sheriff deputies were shot and killed at a Panera restaurant in Harford County.