The man accused of killing 10 people in a racially motivated shooting in Buffalo was given a mental health evaluation last year after making a threatening statement at his high school.
FBI Special Agent Steve Belongia described the shooting at the Tops Friendly Market store as a hate crime and said that the suspect was a racist.
The first time Gendron had visited Buffalo, he was in the city 168 miles from Conklin.
Gendron was brought in by police for a mental health evaluation after making a generalized threat at his high school, but he was not on law enforcement's radar at the time of the shooting.
The Associated Press reported that a law enforcement official said that a man had made a threat to shoot up a Pennsylvania high school around graduation.
Gendron was put on suicide watch after his arrest and is under constant observation because he allegedly put his rifle under his chin.
Gramaglia said that Gendron's parents were cooperative during questioning by the FBI and state police.
Most of the victims of Saturday's shooting were Black, and the attack appeared to be racially motivated, law enforcement officials said. A 180-page manifesto attributed to Gendron claimed the shooting was carried out to generate an "atmosphere of fear and change" in which a white supremacist revolution might take place. Gendron is accused of carrying out the attack while wearing a protective vest and carrying an assault rifle and handguns. The gun shop owner told the New York Times that he sold the gun to Gendron legally in recent months.
Gendron could face life imprisonment without parole if convicted of murder in the first degree.
Wendy Rogers, a member of the far-right group the Oath Keepers, appeared to endorse an unevidenced conspiracy theory that the Buffalo shooting was a government operation. Rogers wrote Saturday on the right-leaning social media platform Gettr that "Fed boy summer has started in Buffalo."
FBI is Probing As Hate Crime after 10 people were shot dead at a supermarket.