JACKSONVILLE, FLA. -- The Jacksonville shooter used to work at a dollar store and stopped in at one before a security guard's presence apparently led him to instead target the Dollar General down the road, where he killed three people.

He worked at a Dollar Tree from October 2021 to July 2022, Jacksonville Sheriff T.K. Waters said at a news conference Monday. And, the sheriff said, he stopped at a Family Dollar store Saturday before pulling into a parking lot at Edward Waters University, where he donned tactical gear. He left when security approached.

"Based off what we saw: him stopping off at the Family Dollar and working at a Dollar Tree previously and then him going to Dollar General, that was his intent the whole time," Waters said. "Why that store? Still hard to tell."

In audio released Tuesday from a 911 call, the gunman's father said his son had stopped taking psychiatric medication and stayed in his room after dropping out of college and losing his job. Other records show the 21-year-old had encounters with police as a teenager, including one involving a suicide threat that led to an involuntary psychiatric evaluation.

Security footage from the Family Dollar shows him walking in and leaving a few minutes later with a small shopping bag. But after he reached his car, Waters said, a security guard pulled into the lot and the shooter left.

Waters believes the guard's presence deterred him. It appeared the shooter wanted to take action at the Family Dollar, but he got tired of waiting, Waters said.

Minutes later, the gunman made his way to the Dollar General in the predominantly Black New Town neighbourhood and killed Angela Michelle Carr, 52, an Uber driver who was shot in her car; store employee A.J. Laguerre, 19, who was shot as he tried to flee; and customer Jerrald Gallion, 29, who was shot as he entered the store. The gunman then killed himself.

The Dollar Tree and Family Dollar chains have the same owner. Dollar General is a separate company.

Zachary Faison Jr., president of Edward Waters University, had said Monday that the security officer, tipped off by observant students, likely stopped the killer from carrying out his racist attack at the historically Black institution. When the officer approached the shooter's vehicle, the driver sped off, hitting a curb and narrowly avoiding a brick column, Faison said.

But Waters said he doesn't believe the university was the intended location for the rampage. He noted two African American males were in the vehicle next to the shooter's in the lot.

Jacksonville is home to nearly 1 million people, one third of whom are Black. The city elected its first Black mayor in 2011.

The weekend shooting happened as the city was preparing to commemorate what it calls Axe Handle Saturday, when a white mob used baseball bats and axe handles to beat peaceful Black demonstrators protesting segregation at a downtown lunch counter on Aug. 27, 1960.

Authorities identified the shooter as Ryan Palmeter, who they said was armed and ready to carry out an attack on Black people. During the attack, authorities said, Palmeter texted his father and told him to break into his room and check his computer.

Waters has said a journal Palmeter's father found in his room was "the diary of a madman" that made it clear he hated Black people.

Forty-five minutes after the shooting began, Palmeter's father called 911 to warn of upsetting messages he had discovered in his son's room, according to heavily redacted audio of the call released Tuesday by the sheriff's office in Clay County, outside Jacksonville.

Details given in the call about the writings, which authorities said included "homicidal and suicidal" threats, were removed from the audio

During the nearly 10-minute phone call, Stephen Palmeter told the dispatcher that his son had stopped taking his psychiatric medication and rarely left his room since dropping out of a local college.

"He doesn't go anywhere," the father said. "He flunked out of Flagler College, moved home a couple years ago, had a job for a while at Home Depot and lost that job, and pretty much has been living in his room."

Additional records released Tuesday by Clay County show Palmeter had at least two encounters with police as a teenager. In 2016, officers responded to a domestic violence call following a physical fight between Palmeter, then 14, and his 20-year-old brother.

The following year, Palmeter fled his parents' home on a bicycle, leaving behind a note indicating plans to take his own life because of stress and painful thoughts. He was taken into custody under a Florida law that allows involuntary psychiatric evaluations for up to 72 hours.

In his writings, Palmeter indicated he was by himself, Waters said Monday.

"I'll tell you, he didn't like anyone," the sheriff said. "He may say that someone he was all right with, and then later on, he will say something disparaging about that group of people. He didn't like government. He didn't like the left or right, if that's what we're talking about. He didn't like anything."

The writings should be released publicly in a week or two, he said.

Palmeter used two guns -- a Glock handgun and an AR-15 style semi-automatic rifle. Authorities said the weapons were purchased legally this year despite once being involuntarily committed for a mental health exam.

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Brumfield reported from Silver Spring, Md., and Offenhartz from New York. Associated Press journalists Valerie Gonzalez in McAllen, Texas, Darlene Superville in Washington, Jake Offenhartz in New York, and Stefanie Dazio in Los Angeles contributed to this report.