CONKLIN, New York — He spent months in his bedroom planning and preparing for his brutal, racist attack at a supermarket that he planned to livestream via a GoPro camera.

He selected his guns in part because he knew the media would obsess over them and modified his assault rifle to carry more bullets. He described both his plans and his clothes in excruciating detail, down to his ill-fitting underwear. He said he’d keep killing until dead or confronted by police.

And over and over and over, he ranted racist beliefs that white people are being replaced by Black and Latinos – a belief system parroted by other mass shooters.

That account, taken from documents, police accounts and personal writings from the suspect, paints a picture of the nation’s latest mass shooter. Although USA TODAY has decided not to quote directly from the suspect’s writings, it is providing general details in an attempt to show how such mass attacks are often planned and carried out, particularly with respect to how weapons and targets are selected. Such general, non-specific details give authorities and the public information that could help citizens spot future mass shooters and even prevent them.

The federal government has repeatedly warned that white supremacist violence is a growing problem nationally, and President Joe Biden a year ago declared that “white supremacy is terrorism.”

Many members of the Black community are angry the shooter seemed to have escaped close scrutiny by law enforcement that spends a disproportionate amount of time policing Black neighborhoods. Like many white mass shooters, Gendron was allowed to surrender to police, instead of being shot dead.

On Sunday, Takesha Leonard of Buffalo cried during a prayer vigil across the street from the Tops Friendly Market Story where the shooting happened.

“I want to know why the government didn’t have no scope on this kid,” Williams said. “The government got a scope on everybody, so why didn’t they have one on this young man that assassinated and killed people?”