A woman killed three people and wounded three others before fatally shooting herself at a drugstore distribution center Thursday in Harford County, Maryland, officials said.
A source close to the investigation said the woman was a disgruntled employee. Sheriff Jeffrey Gahler told reporters the woman was a temporary employee and showed up for work at her normal time at the facility near Aberdeen.
She shot people outside the building and on the warehouse floor, he said. The woman died at a nearby hospital after shooting herself in the head, he said.
Police are still searching for a motive, he added.
A law enforcement official briefed on the incident said the suspect was at some point a security guard at the Rite Aid support facility where the shooting occurred.
The suspect used a 9 mm Glock pistol and brought several magazines for the gun, Gahler said at a news conference. The gun was hers and was purchased legally, he said.
The sheriff wouldn't release any details about the six victims or the shooter, saying that their next of kin were still being notified.
No law enforcement officers fired shots during their response, he said. Johns Hopkins Bayview Medical Center received four patients with "priority one gunshot wounds," said spokeswoman Kristin Mears.
At a news conference, Ray Fang, the hospital's trauma medical director, said two of the victims were stable and doing well, while two remain seriously injured. All the victims were out of surgery, he said.
Fang declined to provide additional information until he was sure all the victims' families had been notified.
Rite Aid spokeswoman Susan Henderson said roughly 1,000 employees work at the distribution center, where products are received and processed for delivery.
"The shooting happened adjacent to the primary building," she said.
Neighbor: 'It's right on the doorstep'
Colleen Hendrickson, who lives and works in the area, said she was waiting on the bus when someone told her there had been a shooting nearby.
"I, of course, thought it was far off or, that's like down the road or something, right?" she told CNN affiliate WJZ. "No, it's right outside. It's right on the doorstep."
She saw emergency vehicles, including ambulances, and helicopters, which were out of place for the "sleepy" part of the county, she said. The area is home to many warehouses and plants, some belonging to major brands, including makeup and bleach companies.
"It's really just usually very calm, and this is the most chaotic I've ever seen it," she told the station. "It's very scary when it's just right there on your doorstep because you can see a billion news reports about shooters, about emergency instances, and it still doesn't make it real to you."
People were being asked to avoid the area just outside the city of Perryman, roughly 30 miles northeast of Baltimore. Homes, churches and a cemetery are in the vicinity. Railroad tracks run alongside a business park.
It's the third high-profile shooting in the US in two days
Deputies were dispatched at 9:09 a.m. ET, the sheriff said. They were on the scene in five minutes.
The Bureau of Alcohol, Tobacco, Firearms and Explosives sent agents from Baltimore. The FBI's Baltimore office is also assisting.
"We are closely monitoring the horrific shooting," Gov. Larry Hogan tweeted. "Our prayers are with all those impacted, including our first responders. The state stands ready to offer any support."
The shooting came a day after two other shootings that made national news. A shooting at an office complex in Middleton, Wisconsin, left three people hurt Wednesday, and a gunman wounded four people at the Masontown Borough Municipal Center in Pennsylvania later in the day.
Police killed the shooters in both Wednesday incidents.
Harford County authorities responded to another fatal shooting in October, when a man killed three people and wounded two others at a remodeling business where he worked in Edgewood. The gunman later drove to Wilmington, Delaware, where he shot and wounded a sixth victim.