A heavily armed 18-year-old white man opened fire at a supermarket in a predominantly black Buffalo neighborhood, killing 10 people and injuring three others, authorities said, in a racist attack that transformed a sunny Saturday on one of the darkest days. in the history of the city.

The suspect was identified in court as Payton S. Gendron of Conklin, New York. He pleaded not guilty Saturday night to first-degree murder, a charge that could lead to life imprisonment without the possibility of parole.

Mr. Gendron was armed with an assault weapon and wearing a bulletproof vest, police said, and he had a video camera attached to his helmet that was streaming the shooting live online.

The attack appears to have been inspired by previous racially motivated massacres, including a shooting at a mosque in New Zealand and another at a Walmart in Texas, both in 2019.

A law enforcement official said investigators were reviewing a manifesto allegedly posted online by Mr. Gendron. It was riddled with racist and anti-immigrant views that asserted that white Americans were at risk of being replaced by people of color, an ideology known as the “great replacement” theory. In the video and footage of the massacre that appeared to be captured by the camera attached to his helmet, an anti-black racial slur can be seen on the barrel of his gun.

Eleven of those shot were black and two were white, authorities said.

“It was a racially motivated hate crime,” Erie County Sheriff John Garcia said at a Saturday night news conference.

The massacre began around 2:30 p.m., authorities said, when Mr. Gendron, who did not live in Buffalo and had driven several hours from Conklin, a town south of Binghamton, to get there, got off his car dressed in tactical gear. equipment and body armor and carrying an assault weapon.

He shot four people in the parking lot, Buffalo Police Commissioner Joseph A. Gramaglia said at the news conference, three of them fatally. When he entered the store and continued shooting, he encountered a security guard – a retired Buffalo policeman who returned fire. But Mr. Gendron was wearing heavy metal plates; he killed the guard and continued into the store, shooting shoppers and employees.

When Buffalo police arrived and confronted Mr. Gendron, he put a gun to his neck, but two patrol officers persuaded him to drop his gun and turn himself in, Mr. Gramaglia said.

U.S. Attorney in Buffalo Trini E. Ross said her office would investigate the killings as hate crimes. Stephen Belongia, the special agent in charge of the FBI’s field office in Buffalo, said the shooting was a “case of racially motivated violent extremism”.

Buffalo Mayor Byron W. Brown said he and his family regularly shop at the store, an outlet of regional chain Tops Friendly Markets. “Some of the victims of this gunman’s attack are people we all know here,” he said, surrounded by the city’s politicians and law enforcement officials.

The attack took place in a neighborhood known as Masten Park on the east side of Buffalo. Dominique Calhoun, who lives near Tops supermarket, said she was parking in her car park when the shooting happened.

She said she saw people running out and screaming, so she parked across the street. She was with her two daughters, 8 and 9, and all three had planned to buy ice cream.

“It literally could have been me,” she said of the people who were killed.

At the crime scene, Barbara Massey Mapps waited anxiously outside the police tape for news of her 72-year-old sister, whom she suspected was in the supermarket at the time of the shooting. “I’ll be here until I see my sister,” she said.

Officials said the camera the shooter was carrying was used to broadcast the attack live on Twitch, an Amazon-owned live streaming site popular with gamers. Twitch said it took the channel offline.

“The user has been indefinitely suspended from our service, and we are taking all appropriate action, including monitoring any accounts reposting this content,” a Twitch spokeswoman said.

Screenshots of the show were circulating online, some of which appeared to show the shooter holding a gun and standing over a body in the grocery store.

Other social media posts showed what was supposed to be a list of instructions the shooter had made himself – a to-do list that included “keep writing the manifesto” and “test the broadcast function live before the actual attack” – on the Discord messaging platform. The Discord username matched the name of the Twitch channel.

Federal authorities are investigating a statement of intent the shooter posted online, according to a senior federal law enforcement official who spoke on condition of anonymity because he was not authorized to release details of the shooting. investigation.

The document, which circulated on the online message board 4chan, compared the shooter’s plan to other bigotry-motivated mass shootings and promoted the “great replacement” theory.

He wrote that he would use a GoPro Hero 7 Black to “live stream the attack on Twitch”, which he chose so “everyone connected to the internet can watch and record”. He noted that the 2019 shooting at a Jewish synagogue in Halle, Germany was also livestreamed on Twitch.

He then went on to detail on more than a dozen pages the tactical gear he recommended for similar attacks, including knives, vests and medical equipment. He said “conservatism is dead” and that progressives’ plea for equality was wrong because, in his view, the average black man had a lower IQ than a white man.

The 10 people killed in Buffalo represent the highest death toll in a mass shooting this year, according to the Gun Violence Archives, which follows them. The highest death toll this year before that was six, in a shooting in downtown Sacramento on April 3. Six people were also killed in a shooting in Corsicana, Texas on Feb. 5, and the same number were killed in a shooting in Milwaukee. on January 23, according to the site.

Gun deaths hit the highest number on record in the United States in 2020, the first year of the pandemic, rising 35%, the Centers for Disease Control and Prevention reported Tuesday.

“This is a historic increase, with the rate reaching the highest level in more than 25 years,” said Dr. Debra E. Houry, CDC’s acting senior deputy director and director of the National Center for Prevention and injury control. a press conference this week.

Dan Higgin, Luke Hammill, Thrush Glenn, Adam Goldman, Alexandra E. Petri, Ashley Southall, Vimal Patel and Eduardo Medina contributed report. Jack Beg contributed to the research.