What we know about the Buffalo mass shooter

What we know:

The suspect livestreamed the shooting on Twitch.

• Twitch, the livestreaming site owned by Amazon, told the New York Times on Sunday that the video was taken down within two minutes of the violence starting.
• Copies and screenshots taken from the broadcast, however, are circulating online.

The shooter wore tactical gear, including a bulletproof vest, and used a semiautomatic rifle during the attack, police said Saturday.

• A supermarket security guard, Aaron Salter, fired at the shooter as he entered the store, but the shots did not penetrate the body armor. Salter, a retired Buffalo police officer, was later killed.
• The rifle used in the attack had a racial epithet scrawled on it and the number 14, a white supremacist numeric symbol.
• The rifle was purchased this year from a vintage gun store near the suspect's hometown, the owner of the gun shop confirmed to NPR.

The suspect drove over 200 miles for the attack.

• Law enforcement officials said Saturday that the alleged shooter drove over 200 miles from Conklin to Buffalo and specifically targeted a grocery store in a predominantly Black neighborhood. Eleven of the 13 people shot were Black.
• Buffalo Police Commissioner Joseph Gramaglia told ABC on Sunday that the suspect was in Buffalo a day before the shooting to "scope out" the supermarket.
• On Monday Gramaglia said "it's now believed" the suspect was in Buffalo in March, not just the day before the shooting.
• Buffalo police on Monday also confirmed the suspect remains incarcerated, in a segregated unit, aside from the general population "for his safety." The police also confirmed the suspect is on suicide watch and undergoing physical and mental evaluation.

The suspect allegedly published racist writings before the attack.

• The police commissioner told reporters on Sunday that state and federal officials had sought warrants for the suspect's home and vehicle as well as computers and phones to obtain details about his online activities.
• Erie County District Attorney John Flynn declined to comment at a Saturday news conference on whether the suspect authored a 180-page screed posted to the online forum 4chan before the shooting, which repeatedly cited the racist and anti-immigrant "white replacement theory" as motivation for the attack.
• A law enforcement official, not permitted to speak publicly, told the Associated Press that authorities were attempting to validate the writing.

Between the lines: There are a number of reports circulating from news outlets and on social media that include details of law enforcement officials speaking on background about details of the attack and ongoing investigation. Axios is working to confirm these reports.

• The Buffalo News, NBC News and other media outlets have seen the document but have not been able to independently verify its connection to the alleged shooter.
• NBC News reporting cites file data accessed, which shows a PDF first posted to Google Docs at 8:55pm on Thursday, but which remains uncorroborated.
• The Washington Post, which refers to the suspect as the author of the document, cited "authorities" who are "scrutinizing" the writing in connection to the attack.

• "Before embarking on a racist rampage in Buffalo on Saturday, the alleged gunman left behind a document denying membership in 'any organization or group,'" the Post writes.

The replacement conspiracy claims the existence of a plot to change America's racial composition by methodically enacting policies that reduce white Americans' political power, Axios' Dan Primack and Russell Contreras report.

• The writings included exhaustive details of a planned shooting, including choosing the highest concentration of Black people nearest to his home, the parking spot he would drive to and the meal he would eat beforehand, according to the New York Times.
• The document calls for the mass killings of Jews and denounces "critical race theory" — an academic framework that examines how U.S. institutions are influenced by historic and present racism — as part of a Jewish plot.
• The suspect said he was inspired by other white supremacist acts of violence, like Dylann Roof, who killed nine members of a Black church congregation in Charleston, South Carolina, in 2015.

The suspect previously threatened to target his high school.

• Gramaglia, the Buffalo Police commissioner, said the suspect, then 17, received a mental health evaluation last June following a "generalized" threat made against his high school, according to the New York Times.
• The suspected gunman was never charged with a crime and there wasn't any additional contact with law enforcement after he was released from the hospital, AP reports.
• "He was evaluated and then he was released," Gramaglia told reporters on Sunday, adding, “There was nothing that was picked up on the state police intelligence, nothing that was picked up on the FBI intelligence."

Go deeper: Remembering the victims of the Buffalo mass shooting

Editor's note: This is a developing story and will be updated with new details throughout.