The Maryland woman who killed three co-workers and injured three others before fatally turning the gun on herself was mentally ill, authorities said Friday.

Snochia Moseley was diagnosed with an unspecified mental illness in 2016, Harford County Sheriff Jeffrey Gahler said during a press conference.

Friends and family of the 26-year-old temporary worker said they’d become “concerned for her well-being” as they noticed she was “increasingly agitated” over the last two weeks, Gahler said.

“There were family members, people close to this person, who had concerns,” he said.

On Thursday, Moseley went to the Rite Aid distribution center in Aberdeen where she’d worked for less than two weeks and fired off 13 rounds from her 9mm Glock handgun, including two at her own head, authorities said.

“The first shot she took was more of a grazing wound and she actually shot herself a second time,” Gahler said.

She died at the Bayview Medical Center.

“She was moving pretty quickly, so not taking a lot of time to aim,” Gahler said. But “You don’t have to be highly accurate when you’re in close quarters.”

Those killed were a 45-year-old man named Sunday Aguda and two women in their 40s, Brindra Giri and Hayleen Reyes, cops said. The wounded included Hassan Mitchell, 19, Wilfredo Villegas, 45, and a 45-year-old woman from New York named Acharya Purna.

Authorities still haven’t determined a motive for the crime, with Gahler saying it’s likely that “there’s never gonna be one.”

Cops have confirmed the weapon Moseley used had been purchased legally in March and was registered in her name.

A community vigil was planned for Friday night at Cranberry United Methodist Church.