Three people were killed in a shooting Saturday afternoon at a Dollar General store in Jacksonville, Florida, that authorities said was racially motivated. The suspect died by suicide, officials said.

In a news conference Saturday evening, Jacksonville Sheriff T.K. Waters said that the suspect, described as a White man in his early 20s, entered a Dollar Store just after 1 p.m. and opened fire, killing three people. All the victims were Black, Waters said. 

"He targeted a certain group of people, and that's Black people," Waters said. 

The suspect then died from a self-inflicted gunshot wound, Waters disclosed. His name was not immediately released.

No one else was wounded in the shooting. The victims, two males and a female, were not immediately identified. 

The suspect was wearing a tactical vest and mask and was armed with a Glock and an AR-15-style rifle, Waters said. There were also swastikas on the guns, he added.

In the news conference, Jacksonville Mayor Donna Deegan called the shooting a "hate-filled crime."

The suspect, who lived in Jacksonville's Clay County with his parents, "authored several manifestos," Waters said, including one to his parents, another to the media, and a third to "federal agents."  At 1:18 p.m. local time, the shooter told his father to check his computer, and by 1:53 p.m., the shooter's family called the Clay County Sheriff's Office, Waters said.

"By that time, he'd already began shooting in Jacksonville," Waters said. 

The gunman's journals "detailed" his "disgusting ideology of hate," Waters said. In them, the gunman also disclosed that the shooting was "racially-motivated, and he hated Black people," added Waters. 

The gunman "acted completely alone" and was not believed to be part of "any large group," Waters said. 

The shooter was previously involved in a 2016 domestic incident for which he was not arrested, Waters disclosed. In 2017, according to Waters, the shooter was also committed under Florida's Baker Act, which is a law that allows law enforcement officers and certain medical personnel to involuntarily institutionalize people who could be considered a harm to themselves or others for up to 72 hours, per CBS Miami.

Officers with the Jacksonville Sheriff's Office and firefighters with the Jacksonville Fire and Rescue Department were on scene investigating, along with members of the FBI. 

The FBI "will pursue this incident as a hate crime," said Sherri Onks, special agent in charge of the FBI Jacksonville Field Office.  

The exact circumstances leading up to the shooting were still unclear. Deegan previously told CBS affiliate WJAX-TV that, following the killings, the suspect had barricaded himself inside the store. 

"One shooting is too much, but these mass shootings are really hard to take," Deegan said from the scene during the standoff.   

Deegan said Saturday night that she was "so sorry we have failed you in the ways we have" to the Black community.

"I will do anything in my power not to do that going forward," she said.

At prayer vigils after the shooting, community members locked arms in unity. Councilwoman Ju'Coby Pittman told WJAX-TV that "this makes no sense." 

"I'm very, very angry right now. I'm emotional, we have kids in this community seeing all of this and this is unnecessary," she said. "It's unjust, we can't walk on the sidewalks, we're not safe in any stores."

Meanwhile, nearby Edwards Waters University said in a campus safety alert during the incident that all students were "kept in their residence halls." The university said the shooting was not believed to have involved any campus faculty, staff or students. 

In a statement provided to CBS News, Dollar General said it was "heartbroken by the senseless act of violence that occurred at our Kings Road store," adding that "supporting our Jacksonville employees and the DG family impacted by this tragedy is a top priority as we work closely with law enforcement."

Attorney General Merrick Garland was briefed on the shooting, CBS News learned. And in a statement, Alejandro N. Mayorkas, Homeland Security secretary, said he has spoken to Deegan and his agency was "closely monitoring the situation."

The attack occurred as tens of thousands of people gathered at the National Mall in Washington, D.C., to commemorate the 60th anniversary of the March on Washington, where in 1963 the Rev. Martin Luther King Jr., made his famed "I Have A Dream" speech.

The Rev. Al Sharpton — who spoke before the National Mall crowd earlier in the day Saturday — said in a statement that the shooter "decided to open fire at a Dollar General while we were marching against hate in Washington."

"Nineteen buses came here from Florida today," Sharpton said of the March on Washington. "Including one from Jacksonville, and while these Floridians were still on the road there was a killing in their home state."

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