Investigators found a small drone in the car owned by the gunman who tried to assassinate former President Donald J. Trump — and believe it was used to survey the site of Mr. Trump’s rally in Butler, Pa., at least once before the shooting, according to law enforcement officials.
Thomas Crooks, 20, visited the area near the fairgrounds used for the rally on July 7 — six days before the event — and appears to have made another trip the morning of the shooting, according to geolocation data found on one of his two cellphones, the officials said.
At some point last Saturday, Mr. Crooks seems to have flown the drone to gather footage for a layout of the Butler Farm Show grounds using a preprogrammed flight path, according to an official briefed on the situation who requested anonymity because the person was not authorized to speak about a continuing investigation.
The discovery of the drone was delayed when investigators found two rudimentary explosive devices in his Hyundai Sonata shortly after Mr. Crooks — a highly intelligent and technologically sophisticated community college graduate — was felled by a sniper after bloodying Mr. Trump’s ear, killing a man in the crowd and seriously injuring two other people.
Investigators also found several magazines for the rifle he used and a bulletproof vest in the vehicle.
Over the past several days, F.B.I. technicians analyzed the drone in its lab, along with two of Mr. Crooks’s phones and other electronic devices in hopes of determining his motive.
