A local law enforcement officer spotted a suspicious man carrying a range-finder "in or just-outside" the venue before former President Donald Trump took the stage at his rally in Butler County, Pennsylvania on Saturday night, according to a law enforcement source.
The officer reported the sighting to state police, the source said. He took a photo, and there was a discussion about whether what he was carrying was a pair of binoculars to try and see the rally better.
A few minutes into Trump's remarks, a would-be assassin identified as Thomas Matthew Crooks, 20, opened fire, according to authorities.
He wounded the former president, killed a 50-year-old father of two and wounded two more spectators before a Secret Service counter-sniper neutralized the threat, according to authorities.
It was not immediately clear how long Crooks was on the roof, but sources say he was initially seen without the gun about 30 minutes before the attack.
State police did not immediately respond to a request for comment on the source's version of events.
Several witnesses have also come forward in interviews and videos on social media claiming they reported seeing an armed man before the shooting started.
"Just because someone is on a roof doesn’t mean the [counter-sniper] guys can just open fire," said Bill Gage, an expert on active shooter response who retired from the Secret Service after 13 years with the agency, including 6 ½ as a member of the counter assault team. "They operate under Graham v Connor use of force rules. They would have had to perceive a threat."
Eventually, however, Crooks made it up onto the roof with DPMS AR-15 5.56 rifle, which authorities recovered at the scene. It had been purchased legally by his father more than a decade ago, according to law enforcement sources.
PENNSYLVANIA TRUMP RALLY SHOOTING SUSPECT PICTURED AFTER DEADLY ASSASSINATION ATTEMPT
Butler County Sheriff Michael Slupe said in interviews with local media that a county deputy confronted Crooks moments before the shooting but ducked for cover when he peered above the edge of the roof and the killer turned the gun on him.
"The officer had both hands up on the roof to get up onto the roof, [and] never made it because the shooter had turned towards the officer, and rightfully and smartfully, the officer let go," he told KDKA-TV.
Security outside the Secret Service's secured perimeter is typically handled by state and local law enforcement.
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The FBI announced earlier Monday that it had broken into Crooks' phone and was examining the device for evidence.
Authorities were also still in search of a motive. They said it appeared that Crooks had acted as a lone wolf, but the investigation was ongoing.
Nearly 100 people, including witnesses and members of law enforcement, had been interviewed as of Monday afternoon.
