Before Thomas Matthew Crooks aimed his AR-15 gun at former US President Donald Trump during a campaign rally in Pennsylvania, his father contacted the police, concerned about his son's location when a gun, one of the many he owned, was missing from their home.
The call, another red flag in a series of warnings to law enforcement before the attack, came from Crooks' father Matthew Crooks after his son disappeared without any notice, a report by BBC said.
While some reports suggest the call happened before the shootingm others suggest Matthew Crooks called police after the shooting.
The gun, used by Crooks in the unsuccessful assassination bid, was identified as his father's 5.56 caliber AR-style rifle which he purchased in 2013, police said. Police sources told NBC that Crooks purchased 50 rounds of ammunition hours before the shooting.
When police searched Crooks' home in Bethel Park, some 85 km from the Trump rally, over a dozen firearms were found inside. As per Pennsylvania law, gun owners do not have to store their firearms in a lock box or other locked storage, but they are encouraged to do so.
Police also found that ahead of the attack, the 20-year-old made several online searches related to Trump as well as his rival US President Biden. He also searched "major depressive disorder" as well as the Democratic National Convention to be held for August.
Reports said police found that he had images of Trump, Biden, Attorney General Merrick Garland, FBI Director Chris Wray and a member of the British Royal Family.
The FBI also found a metal box of explosives in the car which Crooks drove to the rally.
Crooks' motive in the shooting remains unclear but the FBI and other law enforcement agencies have launched investigations. Currently, the FBI are were sifting through Crooks' phone and other electronic devices.
While the motive behind the attack is still unclear, preliminary investigation found that he climbed onto the roof of a nearby building outside the rally, some 300 metres away from where Trump was on stage.
The bullet missed Trump by a few inches but grazed the top of his right ear. Amid chaos and screams, Trump was ushered off stage by Secret Service agents with blood smeared on his face.
