A Texas father helped police thwart a potential mass shooting after he flagged his son’s erratic behavior and violent pronouncements of wanting to “kill many people,” Fort Worth police said.

The father called 911 on Sept. 3 and alerted authorities to his 27-year-old son’s troubling behavior, a department spokesman told the Fort Worth Star-Telegram. His son was off his medication, the father said, and had expressed a desire to buy guns and go on a shooting rampage.

The dad’s call prompted police to track down the man, who the Star-Telegram reported was “well known” to local authorities. By then, he had already visited multiple businesses in an attempt to buy a gun, police said. He was repeatedly turned away, however, after failing background checks for reasons that are unclear.

Police said the man, carrying more than $600, had been trying to buy a gun on the street when they confronted him.

When asked why he was seeking to buy a firearm, “he was just very flat and blunt — to kill people,” said Officer Landon Rollins, a member of a Crisis Intervention Team that confronted the man, according to the Star-Telegram.

“He said, just, ‘I want to kill people.’ He reiterated this many times,” Rollins added. “He was ... not living in reality.”