In the span of 11 terrifying minutes, a gunman targeting Black people killed two shoppers and an employee at a Dollar General store in Jacksonville, Fla., a rampage that the authorities are investigating as a hate crime and that has reverberated through a community that has long coped with the legacy of racism.

The shooting on Saturday, on the same day that the nation commemorated the 60th anniversary of the March on Washington, prompted somber vigils and renewed vows for unity from residents and officials, but also a tense appearance by the governor in a city that in recent years has dealt with a series of hateful incidents and a continuing dispute over Confederate monuments.

“We have three people who are dead because they are Black,” State Senator Tracie Davis, a Jacksonville Democrat, said at a vigil on Sunday morning. “Shopping. In our community. Gunned down. Because they were Black.”

The three victims were identified on Sunday by Sheriff T.K. Waters of Jacksonville as Angela Michelle Carr, 52; Anolt Joseph Laguerre Jr., known as A.J., 29, who worked at the store; and Jerrald De’Shaun Gallion, 19. The sheriff identified the gunman as Ryan Christopher Palmeter, a white 21-year-old from neighboring Clay County and gave a chilling timeline of how the shooting had unfolded.

Ms. Carr, an Uber driver, had dropped off a friend at the store just before she was killed, said her son, Chayvaughn Payne.

“She would give her shirt off her back for people,” Mr. Payne, 30, said, describing Ms. Carr as someone who would invite people to cookouts and other family events.

“This is really hard to process,” he added. “To lose a mother for nothing.”

The gunman, wearing a shirt over a tactical vest, as well as a mask and gloves, began his rampage at around 1:08 p.m. on Saturday by shooting 11 times into a car parked outside the Dollar General, killing Ms. Carr, the sheriff said in a news conference.

The assailant went into the store, turned right and killed Mr. Laguerre before chasing some customers out, though it was unclear why. He returned and killed Mr. Gallion, who had entered through the front door with his girlfriend. The gunman then chased and shot at a woman, though he did not injure her.

When sheriff’s deputies arrived, at about 1:19 p.m., they heard a single gunshot, which was most likely the gunman killing himself, Sheriff Waters said.

“When a person grabs a hold of a gun with hateful intentions, it’s very difficult to stop that from happening,” he said.

The gunman had no criminal record, though the authorities had held him for an involuntary, 72-hour psychiatric evaluation in 2017, when he was 15, the sheriff said. A year earlier, the police received a domestic violence call involving him and his brother.

The gunman legally bought the two weapons he used in the shooting — a Glock handgun and an AR-15-style rifle — in April and June, Sheriff Waters said.

Psychiatric evaluations under a Florida law known as the Baker Act do not show up in background checks unless the person has been committed for treatment.

Shortly before the shooting on Saturday, the gunman was spotted putting on the tactical vest in a parking lot at Edward Waters University, a small and private historically Black institution. A campus security guard saw him, and the gunman drove away in a gray Honda Element. The guard reported the gunman’s suspicious presence to a nearby sheriff’s deputy, Sheriff Waters said.

Two people were in proximity to the gunman in the Edward Waters parking lot, but he did not go after them, the sheriff said, cautioning against assumptions that the university might have been the intended target.

Still, the sheriff said it was clear that the gunman sought Black victims. Most — but not all — of the customers he ordered out of the store were white, the sheriff said at the news conference. In an interview, Sheriff Waters said the gunman did not shoot at one person inside the store who was also white.

“I know for a fact that he did not like Black people,” said Sheriff Waters, who is Black. “He made that very clear.”

Toward the end of the shooting, the gunman texted his father, instructing him to use a screwdriver to get into his room at home, the sheriff said. On the gunman’s laptop, his family found a last will and testament and a suicide note as part of more than 20 pages of racist writings, Sheriff Waters said in the interview. The family then called the Clay County Sheriff’s Office, though by then the shooting was over.

A police car was parked outside the family home in Orange Park on Sunday. Residents of the quiet, suburban neighborhood declined to speak about the family, and relatives could not be reached for comment. Police records indicate that the gunman’s older brother is serving a prison sentence for an armed robbery in 2017.

According to what appears to be an account of the gunman’s on X, formerly known as Twitter, he attended Oakleaf High School. In November 2019, he posted a photo of an acceptance letter from Flagler College. A spokeswoman said on Sunday that he was not currently a student.

The Justice Department is investigating the attack as a hate crime and an act of racially motivated violent extremism. In March, the F.B.I. released an analysis of hate crime incidents in 2021 — the last year data was fully available — which said that hate crimes overall had increased by more than 11 percent since 2020. According to the data, anti-Black hate crimes made up the largest “bias incident category,” with 31 percent of all single-bias incidents in 2021.

Jacksonville, a city of nearly 1 million people, where about 30 percent of residents are Black, has a long history of racism. Sunday marked the 63rd anniversary of Ax Handle Saturday, when white supremacists severely beat a group of mostly Black civil rights activists. Mayor Donna Deegan and other local officials planned to attend a commemorative ceremony in the afternoon, before a vigil for the Dollar General shooting victims.

Last year, on the morning of Sept. 11, a neo-Nazi group unfurled swastika flags and antisemitic banners on an Interstate 95 overpass. And earlier in 2022, homeowners in two neighborhoods found fliers with hate speech littering their driveways.

Last October, an extremist group displayed antisemitic messages around Jacksonville, including at TIAA Bank Field ahead of a Florida-Georgia college football game. Other hateful messages appeared on an Interstate 10 overpass and along another highway.

The Republican-held City Council has declined to remove a Confederate monument from a park, despite pleas from the mayor and a former mayor, who is a Republican, to do so.

“We’re still fighting the same fight, but some days it feels like we’re going backwards,” Ms. Deegan said at the Sunday morning vigil.

In May, Ms. Deegan, a Democrat, was elected to lead Jacksonville, Florida’s largest city, where Republican mayors had been in power for all but four of the last 30 years. Among her administrative appointments was a chief of diversity, equity and inclusion — a $185,000-a-year position that a committee of the City Council voted to defund on Thursday, citing budgetary concerns.

Ms. Deegan blamed state politics under Gov. Ron DeSantis, a Republican running for president, who has enacted laws rolling back diversity and inclusion policies — and whose administration came under withering criticism for rejecting the curriculum of an Advanced Placement African American studies class and rewriting African American history courses.

Mr. DeSantis, who sees public education as too liberal, attended a vigil unannounced on Sunday evening that drew about 150 people. The crowd booed loudly when he was introduced to speak, and a councilwoman had to step in and ask people to listen. After he spoke, he was booed again.

He said earlier on Sunday in Tallahassee that he had talked with Jacksonville officials and with the administration of Edward Waters to ensure the university had adequate security.

“Perpetrating violence of this kind is unacceptable, and targeting people due to their race has no place in the state of Florida,” he said.

The morning vigil, at Saint Paul A.M.E. Church of Jacksonville, was attended by at least four Edward Waters University students. A professor described students as still too overwhelmed to talk about the shooting.

The choir sang “Amazing Grace” as some of those in attendance wiped away tears.

Livia Albeck-Ripka, Alan Feuer, Adam Goldman, Teshia Morris, Nicholas Nehamas and Glenn Thrush contributed reporting. Kitty Bennett contributed research.