BUFFALO, N.Y. (WIVB) – The U.S. Justice Department is investigating Saturday’s mass shooting at a Buffalo supermarket as a hate crime and an act of racially motivated violent extremism.

The gunman was identified during his arraignment as Payton S. Gendron of Conklin, New York. That matches the name given in a 180-page diatribe that surfaced online shortly after the attack and took credit for the violence in the name of white supremacy.

Law enforcement and government officials would not confirm the validity of the document in the immediate hours after the attack. Yet, the excruciating detail provided leaves little doubt of its authenticity. A senior federal law enforcement official told the New York Times they believed Gendron posted the document.

“There are certain pieces of evidence that we have ascertained in the course of this investigation that indicate some racial animosity,” Erie County District Attorney John Flynn said. “I’m not going specifically talk about or elaborate on what exactly they are right now.”

The document, which News 4 has reviewed, plotted the attack in grotesque detail. The writer plotted his actions down to the minute, included diagrams of his path through the store and said he specifically targeted the Tops Markets location on Jefferson Avenue because its zip code has the highest percentage of Black people close enough to where he lives.

“This was pure evil,” Erie County Sheriff John Garcia said. “A straight-up racially motivated hate crime.”

Alexander Rosemberg, deputy regional director for the Anti-Defamation League, says the organization is still sifting through the complete document, but it can already draw some conclusions.

“Greatly antisemitic, greatly racist against people of color, white supremacist, radicalized in all the ways we can think of,” Resemberg told News 4. “180 pages, I want to repeat, of this.”

A diagram included in the shooter’s alleged diatribe plotted a route through the supermarket.

Gendron livestreamed the attack on the social media platform Twitch and had the N-word written on his rifle, videos from the scene showed. He was charged with first-degree murder after killing 10 people and wounding three others.

The alleged diatribe admits to planning the attack passively for the past few years and seriously since January. It bemoans a purported “white genocide” taking place in America and proudly brags of the writer’s racist and antisemitic views.

In a Q&A with himself, the writer says he supports “those that wish for a future for white children and the existence of our people.”

“That’s what white supremacist terrorism is all about — that’s what we witnessed here today,” New York Gov. Kathy Hochul said. “It has to end right here. That is our message. We will continue to work at the federal, state and local level with our community partners to identify these messages as soon as they arise on social media. That is our best defense right now, as well as the legal system and the prosecution. And it is my sincere hope that this individual, this white supremacist who just perpetrated a hate crime on an innocent community, will spend the rest of his days behind bars. And heaven help him in the next world as well.

One of the victims in the attack was identified as Aaron Salter, a retired Buffalo Police officer who was working as a security guard at Tops. Officials said Salter attempted to stop the attack and shot Gendron in the chest, but he was unharmed because he was wearing tactical body armor.

The alleged diatribe carries on for numerous pages about the type of gear that was chosen specifically for the attack, from his helmet and weapon all the way down to his underwear. It plots his breakfast, arrival time, live stream and getaway.

The writer said he will plead guilty in trial if he survives the rampage.

Gendron said only four words in court Saturday before being taken away: “I understand my charges.”

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Note: This story has changed the word “manifesto” to “diatribe,” following guidance from AP’s Stylebook.

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Nick Veronica is a Buffalo native who joined the News 4 team as the Digital Executive Producer in 2021. He previously worked at NBC Sports and The Buffalo News. You can follow Nick on Facebook, Twitter and Threads. See more of his work here.