CONKLIN, New York — He allegedly 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.

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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.

Lemar Williams, who has lived in Buffalo since the 1970s, had planned to take his nephew to work at Tops that Saturday. But his nephew got a call that he didn’t have to go to work that morning — moments later, he found out why. Like many in the neighborhood, Williams wants to know why no one stopped the shooter before he executed the detailed plans he’d posted online.