"Multiple victims. Please avoid the area", the sheriff's office tweeted", after the shooting. Gahler declined to respond to a reporter who asked whether that suggested the suspect's injuries were self-inflicted.
She was in critical condition and later died at a local hospital, police said.
Gahler said Moseley left the warehouse on Thursday morning and drove to her White Marsh home, where she retrieved a handgun, pepper spray and handcuffs.
Johns Hopkins Bayview Medical Center said in a statement Thursday afternoon that it was waiting to confirm that family members have been notified before sharing any additional information.
Two of the those killed died at the scene while the third passed away at hospital. "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".
Cops have confirmed the weapon Moseley used had been purchased legally in March and was registered in her name.
"Our prayers are with all those impacted, including our first responders", Hogan wrote on Twitter.
Federal Bureau of Investigation tactical agents stand ready to assist as police search for a shooter at Thursday's shooting at a Rite Aid warehouse in Maryland, Baltimore on September 20, 2018.
There were no shots fired by the law enforcement officers on the scene.
Authorities respond to a shooting in Harford County, Md., on Thursday, Sept. 20, 2018.
"What I understand is the location is secure", said Rite Aid spokeswoman Susan Henderson.
Mike Carre, an employee of a furniture logistics operation next to the distribution centre where the violence erupted, says he helped tend to a wounded man.
"There's a shooter in the building".
The person was "shooting like insane", Mr Zambrano said, speaking in Spanish.
Also on Wednesday, at least four people were wounded when a software worker shot his fellow employees at a business near Madison, Wisconsin, officials said.