Gendron, 18, traveled about 200 miles (320 kilometers) from his home in Conklin, New York, to Buffalo to commit the attack, police said.
Law enforcement officials revealed Sunday that New York State Police troopers had been called to Gendron’s high school last June for a report that the then-17-year-old had made threatening statements.
The disclosure raised questions about whether his encounter with police and the mental health system was yet another missed opportunity to put a potential mass shooter under closer law enforcement scrutiny, get him help or make sure he didn’t have access to guns.
Gendron had threatened to carry out a shooting at Susquehanna Valley High School in Conklin around graduation, a law enforcement official who spoke on condition of anonymity said. The official was not authorized to speak publicly about the investigation.
Gramaglia said Gendron had no further contact with law enforcement after a mental health evaluation that put him in a hospital for a day and a half.
“Nobody called in. Nobody called any complaints,” Gramaglia said. The threat was “general” in nature, he said, and not related to race.
New York is one of several states that have enacted “red flag” laws in recent years to try to prevent mass shootings by identifying people who show signs that they might be a threat to themselves or others.
Those laws allow law enforcement officers, a person’s family, or in some cases medical professionals or school officials to petition courts to temporarily seize the person’s guns or prevent the individual from buying weapons.
Federal law bars people from owning guns if a judge has determined they have a “mental defect” or they have been forced into a mental institution. An evaluation alone would not trigger the prohibition.
It is unclear whether officials could have invoked the “red flag” regulation after the high school incident. Police and prosecutors wouldn’t provide details on the incident or say when Gendron had bought the weapons used in the deadly attack.