A man armed with a high-powered rifle and a handgun killed three black people at a Dollar General store in Jacksonville, Florida, last night, in what local police described as a racially motivated crime.
The suspect, who has been identified as 21-year-old Ryan Christopher Palmenter, was later found dead.
Palmenter lived with his parents in a suburb of Jacksonville, Sheriff TK Waters told a press conference.
He said authorities believed the gunman acted alone, and that before the shooting he had written "several manifestos" for media, his parents and police detailing his hatred for black people.
"There was no criminal record, nothing," he said, adding that the only thing on file was a domestic violence call with his brother.
"There were no red flags."
Sheriff Waters said the suspect was caught on video shooting the first victim, a black 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 two black men, aged 29 and 19.
Sheriff Waters described his weapons as a Glock and an "AR-15 style" rifle, with swastikas on it, referring to a lightweight semi-automatic long gun often used in mass shootings. He said he wore a tactical vest and his face was covered.
"The hate that motivated the shooter's killing spree adds an additional layer of heartbreak," Sheriff Waters said.
He said the gunman was spotted at a local historically black college, Edward Waters University, where he put on his vest and a mask before going to the local branch of the Dollar General, a discount chain with shops across the US.
Sherri Onks, special agent in charge of the Jacksonville FBI office, said federal officials had opened a civil rights investigation and would pursue the incident as a hate crime.
"Hate crimes are always and will always remain a top priority for the FBI because they are not only an attack on a victim, they're also meant to threaten and intimidate an entire community," Ms Onks said.
US President Joe Biden and Attorney General Merrick Garland were briefed on the incident.
Mass shootings have become commonplace in the US, with more than 469 so far in 2023, the most at this point in the year since at least 2016, according to the Gun Violence Archive.
The non-profit group defines a mass shooting as any in which four or more people are wounded or killed, not including the attacker.
Yesterday's incident in Jacksonville bears similarity to last year's shooting in Buffalo, where a white supremacist killed ten black people.
It took place five years after another gunman opened fire during a video game tournament in Jacksonville, killing two people.
Florida Governor Ron DeSantis condemned the shooting.
"The shooting, based on the manifesto that they discovered from the scumbag who did this, was racially motivated.
"He was targeting people based on their race. That is totally unacceptable," Mr DeSantis said.
