The shooter, Ryan Christopher Palmeter, lived with his parents in a suburb of Jacksonville, Sheriff TK Waters told a press conference. He died of a self-inflicted gunshot wound.

Authorities have described the shooting as racially motivated, saying the man had authored “several manifestos” for media, his parents and law enforcement detailing his hatred for black people.

“There was no criminal record, nothing,” Waters said, adding that the only thing on file was a domestic violence call with his brother. “There were no red flags.”

However, the sheriff said Palmeter was briefly held in 2017 under a state law called the Baker Act, which states a person can be “taken to a receiving facility for involuntary examination” during a mental health crisis.

Reuters could not immediately reach members of the gunman’s family for comment.

The gunman also left a will and a suicide note that were retrieved by his father, the Jacksonville sheriff said.

President Joe Biden noted in a statement on Sunday that the shooting occurred the same day the country marked the 60th anniversary of the March on Washington, the scene of Martin Luther King Jr’s famous “I have a dream” speech.

“We must refuse to live in a country where black families going to the store or black students going to school live in fear of being gunned down because of the colour of their skin,” Biden said.

The Justice Department is investigating the shooting as a hate crime and an “act of racially motivated violent extremism”, Attorney General Merrick Garland said.

Waters said the suspect was caught on video shooting Angela Michelle Carr, a 52-year-old woman, in her car outside the Dollar General, a US discount chain. He then entered the store where he shot and killed 19-year-old Anolt Joseph “AJ” Laguerre Jr and Jerrald De’Shaun Gallion, 29.

Palmeter wore a tactical vest and his face was covered by a mask, Walters said. He carried a handgun and an “AR-15 style” rifle, with swastikas on it, police said, referring to a lightweight semi-automatic long firearm often used in mass shootings.

Authorities said he was spotted trying to enter a local historically black college, Edward Waters University, on Saturday before heading to the Dollar General store.

Palmeter had refused to identify himself to a campus officer and was turned away. “It was later determined that the individual would be involved in a shooting near EWU campus,” the university said.

Florida Governor Ron DeSantis said on Sunday the state would work with the school to ensure it had adequate security following Saturday’s shooting.

A prayer vigil for the three victims took place on Sunday near the location of the shooting.

Saturday’s incident in Jacksonville took place five years after another gunman opened fire during a video game tournament in the city, killing two people before shooting himself.

(Reporting by Maria Caspani in New York and Sarah N Lynch in Washington; Writing by Maria Caspani; Editing by Lisa Shumaker and Bill Berkrot)