(CNN) A woman who shot three people dead at a Rite Aid distribution center in Maryland was a disgruntled employee who had been working there for less than two weeks, authorities said.

Snochia Moseley, 26, opened fire Thursday at the facility near Aberdeen -- the second workplace rampage in the United States in 24 hours.

She killed three people and left three others wounded before turning the gun on herself, authorities said.

"There's just no way to make sense of something that's so senseless," Harford County Sheriff Jeff Gahler said Friday, adding that the motive remains unclear.

A source close to the investigation said Moseley was a disgruntled employee at the facility about 30 miles northeast of Baltimore.

She showed up to work at her normal time

Moseley showed up for work at the warehouse, where she was a temporary employee, at her normal time Thursday morning.

Gahler said she went home at one point and returned later with a handgun, pepper spray and a pair of handcuffs.

She began shooting during break time as some employees headed outside, Gahler said.

About 65 workers were in the warehouse at the time, the sheriff's office said.

Moseley opened fire outside the building and on the warehouse floor. The first victim was shot outside and five others inside the warehouse.

She then fatally shot herself in the head with the same 9 mm Glock pistol, Gahler said.

Witnesses told investigators that Mosely shot herself twice, with the first shot grazing her head, the sheriff said.

Gahler said Mosely had been diagnosed with a mental illness in 2016 and that her friends and family members reported that in recent weeks she had become "increasingly agitated and that they were concerned for her well-being."

Deputies were dispatched at 9:09 a.m., he said. Within five minutes, he said, deputies were at the scene, along with the FBI, state police, first responders and other law enforcement authorities.

"You can't have enough police, and you can't have them fast enough, Gahler said.

The sheriff's office identified the victims as Sunday Aguda, 45, from Baltimore County; Brindra Giri, 41, also from Baltimore County; and Hayleen Reyes, 41, of Baltimore.

The injured were identified as Hassan Mitchell, 19, of Harford County; Wilfredo Villegas, 45, of Montgomery County; and Acharya Purna, 45, from New York.

In a statement, Rite Aid said the distribution center has been closed and grief counselors were made available to employees.

"Our thoughts and prayers go out to all those involved in this tragic incident, as well as their loved ones."

Mother texted daughter when gunfire broke out

When the gunfire erupted, Alexie Scharmann got a series of text messages from her mother, who works at the facility.

"I love you ... more than you'll ever know," her mother said.

. "Be good and take care of dad (and) the pets if something should happen." "There's a shooter in the building. I'm hiding. I love you," she texted, according to CNN affiliate WBAL . "Be good and take care of dad (and) the pets if something should happen."

Scharmann's mother survived and sent her the text message she had been hoping for at 10:33 a.m.

"I am outside and safe. I love you," it said.

Shooter was a former security guard

Gahler said Mosely once was a security officer but not at the Rite Aid distribution center. She had a Maryland handgun permit that expired in May.

She used a gun she purchased legally, Gahler said, adding that no law enforcement officers fired shots during their response.

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.

Colleen Hendrickson, who lives and works in the area, was waiting for a bus when the shooting started.

"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, ambulances and helicopters rush to the scene.

"It's really just usually very calm, and this is the most chaotic I've ever seen it," she told the station.

Three shootings in two days

A day earlier, two other shootings made national news.

Police killed the shooters in both cases Wednesday.