Authorities have released details from a 911 call made by the father of Ryan Christopher Palmeter -- the gunman who killed three people in what authorities called a racially motivated rampage at a Dollar General store in Florida.

Palmeter, 21, opened fire at the store in Jacksonville on Saturday before killing himself. He had a swastika-emblazoned assault-style rifle and left behind racist writings, officials said.

After the gunfire started, Palmeter texted his father and told him to go into his room, where the father found a will and a suicide note, Jacksonville's sheriff said.

At 1:53 p.m., Palmeter's father told a 911 operator that his son left the house a couple of hours before the call, according to redacted details from the Clay County sheriff's office.

Palmeter had been getting psychiatric help and was on medication, but it looked like his son had stopped taking his medication because there was a full bottle that was filled on July 23, his father told the operator.

The father also said he called the Clay County sheriff's office a few years ago when his son threatened to kill himself.

Palmeter flunked out of college, then worked at Home Depot and was "pretty much been living in his room" after losing that job, his father told the operator.

But by the time the father learned what was happening and called 911, it was too late. His son had already gunned down three victims: Anolt Joseph "AJ" Laguerre Jr., 19; Jerrald Gallion, 29; and Angela Michelle Carr, 52.

While the families grieve, the Justice Department is investigating the shooting as a hate crime and an act of racially motivated violent extremism, US Attorney General Merrick Garland said.

Here's the latest on what we know about the investigation:

The gunman went to an HBCU right before the killings

Less than an hour before the deadly rampage, Palmeter drove to the parking lot of Edward Waters University -- the first historically Black college or university in Florida, the school's president and CEO said.

That's where students noticed Palmeter putting on a tactical vest, gloves, a mask and a hat, campus security officer Lt. Antonio Bailey said. The students quickly notified security.

"We knew that he was not supposed to be on the university campus," Bailey said.

University security pursued Palmeter until he drove off campus, Bailey said. They then flagged down a Jacksonville sheriff's officer to report the suspicious person, Sheriff T.K. Waters has said.

About 10 minutes after leaving the university, the gunman opened fire in a nearby Dollar General parking lot and throughout the store before fatally shooting himself, authorities said.

The violence happened on the same weekend as the 63rd anniversary of Ax Handle Saturday -- when more than 200 White rioters in Jacksonville chased and beat Black residents with baseball bats and ax handles, according to the Zinn Education Project.

The shooter left behind writings to his parents, the media and federal agents outlining his "disgusting ideology of hate," the Jacksonville sheriff said.

Investigators believe the gunman originally intended to attack a different dollar store -- a Family Dollar he visited just minutes before driving to the university, Waters told CNN's Abby Phillip on Monday night.

Waters believes the sight of a security vehicle arriving at the store and parking outside deterred the shooter.

"I don't think he wanted to have any confrontation with someone that would create an issue for him or stop him from doing what he wanted to do," Waters said.

"He had a goal in mind," the sheriff said. "I think he wanted those stores -- one of those stores. I don't know why."

More details about the timeline emerge

It took less than an hour for the gunman to travel from the Family Dollar -- where investigators believed he initially planned to carry his attack -- to nearby Edward Waters University and then to the Dollar General where he killed three victims, according to the Jacksonville Sheriff's Office.

The shooter, who lived with his parents in the town of Orange Park in Clay County, left his home around 11:39 a.m. Saturday and drove to Jacksonville in neighboring Duval County, Waters said.

At around 12:23 p.m., surveillance footage shows he pulled into the Family Dollar, where he went inside to buy a few items and then returned to his vehicle at 12:29 p.m., the sheriff said.

About a minute later, a security vehicle pulled into the lot and parked in front of the store. The shooter waited for a few minutes and drove away at 12:39 p.m.

He stopped at Edward Waters University at 12:48 p.m. and began putting on a bulletproof vest, Waters said.

Surveillance footage shows two young African American men getting into the car next to the suspect's as he was sitting in the lot, the sheriff noted. That bolsters Waters' belief that the gunman didn't intend to carry out an attack at the university, he said.

"He had the opportunity to do so, and he did not," Waters told CNN on Monday.

The shooter immediately started to drive away after being approached by a security officer, and he was followed until he left campus, Edward Waters University President and CEO A. Zachary Faison Jr. said.

He left the lot around 12:58 p.m., according to the sheriff. Campus security then flagged down a sheriff's officer, to report the suspicious activity, he said.

Within minutes the gunman pulled into the Dollar General parking lot. At 1:08 p.m., he shot into a black Kia in the lot, killing Carr, the sheriff said. He then entered the store and fatally shot Laguerre, the sheriff said.

The gunfire sent people fleeing out the back of the store, followed by the shooter seconds later, the sheriff said. He then came back inside and shot at security cameras.

The first 911 call was at 1:09 p.m., seconds before the third victim -- Gallion -- walked into the store with his girlfriend. The gunman then fatally shot Gallion and chased after another person, whom he shot at but didn't hit, the sheriff said.

At 1:18 p.m., the gunman texted his father and told him to go into his room, where the father found a will and a suicide note, the sheriff said.

Officers entered the store a minute later -- 11 minutes from the start of the shooting -- and heard one gunshot, which is presumed to be when the gunman shot and killed himself, the sheriff said.

A 4-year-old girl loses her father

Gallion's grieving family said didn't know how to tell his 4-year-old daughter that her father is never coming home.

"I thought racism was behind us. But evidently, it's not," said Sabrina Rozier, a grandmother of Gallion's young daughter.

Dollar General identified one of the victims, Laguerre, as an employee of the store.

"The DG family mourns the loss of our colleague Anolt Joseph "AJ" Laguerre, Jr., who, along with two of our customers, were the victims of senseless violence yesterday," the company said in a statement to CNN.

"We extend our deepest sympathies to their families and friends as we all try to comprehend this tragedy. There is no place for hate at Dollar General or in the communities we serve."

Florida State Sen. Tracie Davis represents the area where the shooting happened and said the premeditated, racist attack is a devastating sign of the times. "I'm angry," Davis told CNN. "I'm sad to realize we are in 2023 and as a Black person we are still hunted, because that's what that was."