Eerie photo of Trump shooter's bike left at rally site as expert questions why 'flying squad' wasn't mobilized

BUTLER, Pa. — A lone bike cloaked by a tree's shade near a Pennsylvania manufacturing facility is a haunting reminder of a gunman's hail of gunfire that nearly assassinated a former president.

The shooter, Thomas Matthew Crooks, rode the bicycle to Donald Trump's rally in Butler and ditched it before he opened fire from a roof about 150 yards from where the former president spoke to the crowd of thousands on Saturday, The New York Post reported.  

Crooks left the bike behind in plain sight before he climbed to his perch and unfurled a flurry of gunshots that killed a local hero, who shielded his family, nicked Trump's ear and wounded two others. 

A witness first noticed the bicycle around 5:30 p.m. on July 13 – about 42 minutes before the shooting – according to The Post. The security misstep has at least one expert believing "someone was asleep at the switch."

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Paul Mauro, an attorney and retired NYPD inspector who has been involved in several multi-agency security coordination efforts during his career, said a "flying squad" should have nabbed Crooks well before he pulled the trigger. 

A "flying squad," which can have different names, is an untethered, mobile response team that acts as roving surveillance and chases down anything suspicious. 

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Crooks was first identified as a "suspicious person of interest" around 5:10 p.m., the FBI told Congress, according to a lawmaker who was at Wednesday's FBI briefing and spoke to Fox News Digital on the condition of anonymity.

At 5:30 p.m., a witness spotted Crooks with a rangefinder. Other rally attendees reported Crooks' suspicious movements to police. 

But stationed law enforcement officers can't leave their posts, in case the suspicious person or item is meant as a diversion, Mauro explained. That's why there's a separate team. 

"A lot of people have been saying, ‘Why didn’t they go chase them down an hour before the event?' When you're that close to event time, you have to guard against a diversion," Mauro told Fox News Digital. 

"Somebody sets something off as a diversion, and now the principal is left unguarded."

In this particular case, that would have been Trump. 

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"So you're supposed to remain at your post. The way to assuage that rigidity is to have a flying squad," he said. "They'll get reports that x, y, z have been noticed, get a flying squad over there forthwith.

"And if you're really concerned about him an hour before the event, you make sure you keep eyes on him … but somebody was asleep at the switch."

At 5:52 p.m., the Secret Service spotted Crooks on the roof, the FBI told Congress, according to a lawmaker.

Twenty minutes later – 6:12 p.m. – Crooks fired several shots into the crowd. 

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One bullet nicked Trump's ear, and it may have killed him if Trump hadn't moved his head at that exact moment.

A beloved former fire chief, Corey Comperatore, died while shielding his wife and daughters from a hail of bullets, and two other men were seriously wounded. 

Crooks was ultimately shot dead after nearly 30 seconds of gunfire. 

Nearly a week after the shooting, there are many unanswered questions, including how Crooks slipped through the cracks and was allowed to fire so many times into the crowd. 

There were apparent lapses in planning and/or execution of a safety plan that have to be addressed, Congress members told Fox News Digital. 

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Crooks reportedly rode the bike to the park, sources told The New York Post, but he was also connected to a white van that law enforcement sources said contained explosive materials. 

But what he used and when remains a mystery. 

Butler Township police referred questions to the FBI, Secret Service and Pennsylvania State Police. 

The FBI had no comment, and the Secret Service and state police didn't respond to Fox News Digital's requests for comment. 

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That continues law enforcement's radio silence since Saturday's attempted assassination.

A witness first noticed the bicycle, which was still propped up by a backpack, around 5:30 p.m. on July 13, 42 minutes before the shooting, according to The Post.