A number of people were shot and killed on Thursday at a Rite Aid distribution center in Perryman, Maryland, and the suspected shooter was in custody and critical condition, the county sheriff said.
The shooting occurred shortly after 9 a.m. EDT (1300 GMT) in Perryman, about 34 miles (55 km) northeast of Baltimore.
"I can confirm multiple wounded and multiple fatalities," Harford County Sheriff Jeffrey Gahler told reporters at a news briefing, without offering a specific number. He did not provide any details regarding the suspect's identity or possible motive behind the shooting.
An NBC reporter, Pete Williams, said multiple law enforcement sources told him the shooter was a woman.
A law enforcement source told Reuters that officials believe the suspect had a work-related grievance.
The suspect used a single handgun, the sheriff said, and no officers fired any shots at the scene. He declined to respond to a reporter who asked whether that suggested the suspect's injuries were self-inflicted.
The Rite Aid center sits among a number of warehouses. The facility has nearly 1,000 employees, company spokesman Pete Strella said, and processes products, including pharmaceuticals, for delivery to more than 2,500 stores.
The shooting took place a few miles from the Aberdeen Proving Ground, a large Army facility where military technology is developed and tested, according to Harford County's website.
Governor Larry Hogan said his office was "closely monitoring the horrific shooting."
"Our prayers are with all those impacted, including our first responders," Hogan wrote on Twitter. "The State stands ready to offer any support."
Agents from the Baltimore offices of the 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.
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