BREAKING: Sniper noticed Trump shooter Crooks 90 MINUTES before attempted assassination

Text messages revealed that law enforcement responsible for monitoring former President Trump's Pennsylvania rally spotted his would-be assassin and flagged him to colleagues as suspicious at least 90 minutes before he opened fire.

The messages, obtained by Fox News Digital from Sen. Chuck Grassley, R-Iowa, who obtained them from Beaver County Emergency Services Unit, showed that officers flagged 20-year-old Thomas Matthew Crooks after he was spotted using a range finder – but did not approach him.

The first screenshot is a group chat of Beaver ESU officers, while the second is from one Beaver County sniper departing his shift at around 4:30 – approximately an hour-and-a-half before Trump took the stage. The New York Times first reported the text screenshots.

In a group chat, around 4:36 p.m., when one of the officers texted that his shift was ending, he warned that a man, later identified as Crooks, had parked nearby their vehicle.

"Someone followed our lead and snuck in and parked by our cars just so you know," the text from an officer read.

A follow-up message said that Crooks was about 50 yards from the rally's exit, sitting at a picnic table.

Two other counter-snipers responded with a thumbs up emoji and responded, writing, "Roger that."

Approximately 45 minutes later, at 5:10 p.m., officers flagged that Crooks was on the move and had positioned himself near the American Glass International (AGR) building. Crooks would later perch himself on top of the AGR building to target the former president.

The picture showed Crooks leaning against the AGR building with his signature greasy shoulder-length hair and gray t-shirt.

"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."

"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."

The FBI on Monday morning told reporters that would-be Trump assassin Thomas Crooks accessed the roof of a building near former President Trump's July 13 rally in Butler, Pennsylvania, by climbing up HVAC equipment and piping.

Crooks then traversed multiple rooftops before he found his shooting position on top of a building owned by American Glass Research (AGR), located near the Butler Farm Show fairgrounds about 150 yards from where the former president spoke at his rally.

The FBI hosted a press conference call with reporters more than two weeks after 20-year-old Crooks fired at Trump with a DPMS AR-15-style firearm with a collapsable stock during the rally in an assassination attempt that nicked the president's ear but left one man dead and two others hospitalized with gunshot wounds.

Kevin Rojak, special agent in charge at the FBI's Pittsburgh field office, said the agency has examined more than 2,100 tips related to the assassination attempt since July 13.

Leading up to the shooting, Crooks apparently conducted internet searches for current and former presidents.

The Trump campaign announced the Butler rally on July 3, and three days later, Crooks signed up for the event. That same day — July 6 — he researched how far Lee Henry Oswald was from the late President John F. Kennedy when Oswald assassinated the former president in 1963. On July 7, he traveled to the rally site and spent approximately 20 minutes in the area, Rojak said.

On the day of the rally, Crooks parked his vehicle and flew a drone between about 3:50 p.m. and 4 p.m. about 200 yards from where the former president would be speaking on July 13. FBI Director Christopher Wray testified during a July 17 congressional hearing that Crooks had been at the rally site for about 70 minutes the morning of the assassination attempt.

It is still unclear how Crooks evaded security even after being noticed by law enforcement more than an hour before shots rang out, but the FBI said more than 300 agents and staff are working "round the clock" to gather facts and put together a clearer timeline of Crooks' actions.

Investigators located eight rounds on the roof where Crooks fired from, the agency said during the call.

Law enforcement first reported seeing a suspicious person near the rally site around 5:10 p.m. on July 13 — an hour and one minute before Crooks began shooting. Local law enforcement notified command about the suspicious person and received confirmation that the Secret Service was aware of his presence.

Subscribe to LiveNOW from FOX!

Where to watch LiveNOW from FOX

Follow us @LiveNOWFOX on Twitter

Raw and unfiltered. Watch a non-stop stream of breaking news, live events and stories across the nation. Limited commentary. No opinion. Experience LiveNOW from FOX.