Trump assassination attempt: Thomas Crooks surveyed grounds, used drone with law enforcement in position

The man who attempted to assassinate former President Trump and successfully killed one of his supporters in Butler, Pennsylvania, scoped out the sight of the July 13 rally while local law enforcement officers were in position.

A detailed timeline and accompanying text messages, obtained by Fox News Digital from Sen. Chuck Grassley, R-Iowa, who obtained them from the Beaver County Emergency Services Unit (ESU), provided additional details that led to Thomas Matthew Crooks' successfully setting up his AR-styled rifle and opening fire.

According to a timeline released by the Beaver County ESU, local law enforcement officers were in their pre-determined places at 10:15 a.m. and local snipers were in place by 10:30 a.m. on Saturday, July 13.

Images of the Beaver County ESU showed the sniper's positioning among the buildings at the Butler Farm Show grounds.

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Emerging details of Crooks' whereabouts prior to the shooting placed the 20-year-old surveying the scene at the same time local law enforcement officers and local snipers were in position.

The FBI previously revealed that Crooks, at 11 a.m. on July 13, had driven to the rally site and spent an hour there before heading home.

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Crooks did not return to the scene until 3:50 p.m. Local law enforcement officers, in their designated positions, spotted him for the first time around 5:10 p.m. — approximately 50 minutes before Trump took the stage, according to documents provided by Grassley's office.

On his return to the rally site, Crooks flew a drone about 200 yards away from where Trump was going to be speaking, according to the FBI.

The FBI later said that no photos or videos were taken from the drone and that the agency found no memory card in the drone.

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At 5:30 p.m., local law enforcement snapped a picture of Crooks and escalated it to command. 

"Kid learning around building we are in," an officer wrote in a text message, along with an image of Crooks. "AGR I believe it is. I did see him with a range finder looking towards stage. FYI. If you wanna notify SS snipers to look out."

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"I lost sight of him," the officer added.

A follow-up message said: "Call it in to command and have a uniform check it out."

By 6:12 p.m., the "kid" would be killed by a counter-sniper after he opened fired on the rallygoers.

Trump was grazed by a bullet on his ear, while three rallygoers were also shot, including Corey Comperatore, 50, who was killed protecting his family from danger.

David Dutch and James Copenhaver were injured after being shot at the rally. They have both since returned home.