The gunman who tried to assassinate former US President Donald Trump fired at least eight shots and launched a drone at the site of a campaign rally in Butler, Pennsylvania, about two hours before it began, Federal Bureau of Investigation chief Christopher Wray said Wednesday, according to NBC News.

Thomas Crooks, 20, launched the drone about 200 yards from the event's main stage around 4 p.m. July 13, Wray said at a U.S. House Judiciary Committee hearing.

Authorities found the drone in Crooks' car, where they also found a drone controller and two explosive devices that could be detonated remotely, Ray said.

Crooks was carrying a transmitter, the FBI director said, adding that it appeared a remote detonation “would not have worked.” Eight shell casings were found on the roof along with the gunman's body, he said. According to Ray, Crooks bought a ladder about 5 feet (1.5 m - ed.) high, but it was not found at the scene.

“It is not known if he used the ladder to climb onto the roof,” he said. Ray is expected to continue testifying Wednesday about the FBI's investigation into the shooter's motives and training.