Originally Published: 15 MAY 22 01:37 ET

Updated: 16 MAY 22 12:35 ET

By Shimon Prokupecz, Artemis Moshtaghian, Christina Maxouris, Samantha Beech and Dakin Andone, CNN

(CNN) -- The 18-year-old man who allegedly shot and killed 10 people in Buffalo Saturday afternoon was motivated by hate, authorities said, targeting a supermarket in the heart of a predominantly Black community.

Eleven of the 13 people shot by the White suspect at the Tops Friendly Market were Black, officials said. Among the victims, who range in age from 20 to 86, are a heroic former police officer who tried to stop the gunman, mothers and aunties grocery shopping for their loved ones, a long-term substitute teacher and a taxi driver who "took pride in helping people."

"This was pure evil," Erie County Sheriff John C. Garcia said Saturday, calling the shooting a "straight up racially motivated hate crime from somebody outside of our community."

The US Department of Justice is investigating the shooting "as a hate crime and an act of racially-motivated violent extremism," according to a statement from US Attorney General Merrick Garland.

Payton S. Gendron of Conklin, New York, was charged with first degree murder Saturday, Erie County District Attorney John J. Flynn said in a news release. He has pleaded not guilty.

Here's what we know about the shooting suspect.

He planned to 'continue his rampage,' police say

Authorities say when the suspect arrived at the store around 2:30 p.m., he was heavily armed, wearing tactical gear, a helmet and had a camera that was livestreaming his actions.

The suspect used an assault weapon, Flynn said during a news conference.

The suspect shot four people outside of the grocery store, three fatally, Flynn said in his news release. When he entered the store, he exchanged fire with an armed security guard, who authorities said was a retired Buffalo police officer. The security guard died of his injuries. The suspect shot eight more people in the store, six of whom died, the release said.

Confronted by police, the suspected shooter took off some of his tactical gear and surrendered, per Buffalo police.

The suspect planned to continue his shooting rampage beyond the Tops supermarket, Buffalo Police Commissioner Joseph Gramaglia told CNN Monday, saying there was "some documentation" he allegedly planned to target "another large superstore."

"There was evidence that was uncovered that he had plans, had he gotten out of here, to continue his rampage and continue shooting people," Gramaglia said in an interview. "He'd even spoken about possibly going to another store."

The suspect made very disturbing statements describing his motive and state of mind following his arrest, an official familiar with the investigation told CNN.

The official said the statements made after the arrest were clear and filled with hate toward the Black community. The alleged shooter made it known he was targeting the Black community during the statements, according to the official.

Investigators have uncovered information from search warrants and other methods indicating the alleged shooter was "studying" previous hate attacks and shootings.

Document talks about 'dwindling size' of White population

Investigators are going through a 180-page document posted online for clues, Flynn said. Officials have described the document as a purported "manifesto" allegedly written by the suspect.

"We are obviously going through that with a fine-toothed comb and reviewing that for all evidence that may lead us to besides the manifesto itself," the DA told CNN Sunday afternoon.

"All the evidence that we ascertain from that manifesto, from wherever that manifesto leads us, other pieces of evidence we already had, we can then use that and develop more charges potentially," he added.

The document, independently obtained by CNN shortly after the attack and before authorities released the suspect's name, is allegedly written by a person claiming to be Payton Gendron confessing to the attack.

The author attributes the internet for most of his beliefs and describes himself as a fascist, a White supremacist and an anti-Semite.

The author bought ammo for some time but didn't get serious about planning the attack until January, per the document. The author also writes about his perceptions of the dwindling size of the White population and claims of ethnic and cultural replacement of Whites.

According to the document, the suspect allegedly chose to attack the Tops Friendly Markets store in Buffalo because it was in a majority-Black ZIP code within driving distance of where he lived, and he researched what time it would be busiest.

The ZIP code that includes the store, 14208, is 78% Black -- the highest percentage of Black population of any ZIP code in upstate New York -- per the US Census Bureau's 2020 American Community Survey. Conklin, where the suspect is from, is a three-and-a-half-hour drive from Buffalo.

He made 'generalized threat' at high school in 2021

Gendron made a "generalized threat" while he attended Susquehanna Valley Central High School in June 2021, Buffalo Police Commissioner Joseph Gramaglia said Sunday.

In response to a question from CNN's Shimon Prokupecz at a Buffalo news conference, Gramaglia said state police brought the student in for a mental health evaluation. After a day and a half, he was released, according to Gramaglia.

The threat was not racially motivated, Gramaglia said.

Sheriff Garcia told CNN Monday the suspect was visited last year by New York State Police after he did a high school project about murder-suicides.

According to Garcia, concerns about alleged mental health issues "were brought to light" after he turned in the post-graduation project.

"The state police arrived at his house at that point last year," Garcia said. "He stayed at a facility -- I'm not sure if it was a hospital or a mental health facility -- for a day and a half."

Separately, a spokesperson for New York State Police told CNN Sunday it investigated a report that a 17-year-old student had made "a threatening statement." The student was taken to a hospital in June 2021 for a mental health evaluation.

State police responded to Susquehanna High School in Conklin, NY, on June 8, 2021, following the threatening statement, the spokesperson said.

"The student was taken into custody under NYS Mental Health Law section 9.41 and transported to the hospital for a mental health evaluation," state police told CNN in an email.

State police were unable to confirm how long the individual was in the hospital or the findings of the evaluation. They also refused to name the 17-year-old.

Gendron was a worker at the local Conklin Reliable Market for about four months before he left about three months ago, according to the store's owner. The owner of the store says he was very quiet and left on his own terms, giving two weeks' notice.

Neighbors say they would see Gendron's mother regularly walking in the neighborhood. One neighbor said the mother was a nice woman, and they "never would have thought that in a million years" Gendron would have racist views. The neighbor added, "It's pretty shocking."

Another neighbor said when you talked to Payton Gendron, "you wouldn't get more than a word or two" from him.

Gun was legally purchased in New York state, governor says

It's not clear if the suspect should have been prevented from being sold a gun in New York state, New York Gov. Kathy Hochul said Sunday, after it's emerged the gunman was once investigated over something he had written in high school.

Earlier Sunday, Hochul told CNN the gun used in the Buffalo mass shooting where 10 people were killed on Saturday was purchased legally in New York State. In an interview with CNN's Dana Bash on "State of the Union," Hochul described the weapon as an AR-15. It's believed the high-capacity magazine was purchased outside of New York, the governor added.

Speaking to Margaret Brennan on CBS' "Face the Nation" Sunday, Hochul was asked how the 18-year-old suspect was able to legally purchase a gun, given the fact he had been investigated for past comments.

"That is exactly what is being investigated now," Hochul responded. "I understand that he wrote something when he was in high school and that was being investigated. So we're going to get to the bottom of that."

Asked by Brennan if the sale of the gun was an oversight by the State, Hochul said, "We don't know that right now. But I'm going to get to the bottom of it and find out right now. It would have happened a while back."

He allegedly livestreamed on Twitch

The shooting suspect used the popular livestreaming platform Twitch to stream a live broadcast during the attack, the company confirmed Saturday.

The company was "devastated" to hear about the shooting, it said, adding the user "has been indefinitely suspended from our service, and we are taking all appropriate action, including monitoring for any accounts rebroadcasting this content."

CNN obtained a portion of the livestream showing the alleged shooter pulling up to a Tops store.

The video is recorded from the point of view of the alleged shooter as he is driving into the supermarket's parking lot. The person is seen in the rearview mirror wearing a helmet and is heard saying, "Just got to go for it," before he pulls into the front of the store.

In the video, store patrons can be seen walking through the parking lot as the suspect drives up.

A spokesperson for Twitch said the company removed the livestream less than two minutes after the violence started. The company did not immediately respond to follow-up questions about whether the suspect was actively firing when the livestream was halted.

He will likely face more charges

The suspect was arraigned Saturday evening before Buffalo City Court Chief Judge Craig Hannah on one count of first-degree murder, the district attorney's news release said.

He pleaded not guilty, Hannah told CNN. If convicted, he faces a maximum sentence of life in prison without parole, the release said.

And there may be more charges coming, officials said.

"My office is working closely with the U.S. Attorney's Office and our partners in law enforcement into potential terrorism and hate crimes. This is an active investigation and additional charges may be filed," Flynn said in a statement.

Gendron is set to return to court on the morning of May 19 for a felony hearing, the release said. He will remain in custody without bail, it added.

He is likely the "most highly visible incarcerated individual" in the country, Erie County Sheriff Garcia told CNN Monday. There are video cameras in his cell, and he remains under watch by an Erie County sheriff's deputy at all times, Garcia said.

"He's in a unit with no commingling with other incarcerated individuals," Garcia added.

Meanwhile, authorities continue to investigate the suspected shooter. Investigators are collecting evidence from the crime scene, the home he lived in with his parents, the car he used and his history on social media, the DA said.