(NewsNation) — In a 180-page manifesto believed to be written by the alleged Buffalo supermarket shooting gunamn and posted online before the masacre, he claims he was bored in May 2020 during the pandemic and started watching and listening to white supremacist ideology on the internet, which led him to becoming radicalized. One website, in particular, was his go-to place to find like-minded people.

Last June, investigators say, suspect Payton Gendron threatened to shoot at his high school graduation. The police investigated, and Gendron was ordered to undergo a mental health evaluation, which produced no red flags or immediate concerns.

New York has some of the toughest gun laws in the country. The state’s Red Flag Law bars people with a mental health diagnosis and deemed dangerous and a threat to others from buying or owning a firearm. But Gendron was never officially labeled a threat, according to investigators.

And because he was not charged with anything related to that threat, Gendron was free and clear.

“A lot of times, it’s that we don’t see the full picture until after an act of targeted violence has occurred,” board-certified psychologist Dr. Katie Kuhlman said.

“Once a person is on your radar as being concerned, they need to always remain there,” she added.

At least 19 other states across the country have similar red flag laws. In 2020, the Wall Street Journal reported authorities around the nation used red flags to temporarily remove 5,000 guns from people.

Investigators say Gendron knew where the highest concentration of African-Americans lived in Buffalo. He traveled 200 miles to the city use an AR-15 that he purchased legally to kill as many Black people as he could before surrendering to police. A total of 10 people were killed in the attack.

Why is it that an 18-year-old with a mental health history can buy an AR-15? Why does that happen? Now, Peyton Gendron may have purchased that rifle he used legally, but investigators say the high capacity magazines he allegedly used with the gun are illegal. Authorities are now trying to determine where he actually purchased those magazines.

New York Gov. Kathy Hochul said she plans to launch an investigation to take a more detailed look at why Grendon slipped through the legal system and would eventually go on to commit one of the worst mass murders New York state has ever seen.

Gendron’s parents, who were both New York state employees, have been cooperating with investigators.