(NewsNation) — A member of local law enforcement saw the gunman who attempted to assassinate former President Donald Trump during a campaign rally in Butler, Pennsylvania, more than 90 minutes before the shooting started.

The New York Times obtained text messages written by a local countersniper who was part of the broader security detail during the July 13 rally.

At 4:19 p.m. that day, the countersniper let his colleagues know his shift was ending. A few minutes later, he texted them again to say there was a young man with long stringy hair sitting on a picnic table outside the fenced area of the Butler County Fairgrounds.

The countersniper confirmed to the New York Times the individual he was texting about was the gunman, Thomas Crooks. Republican Sen. Charles Grassley of Iowa provided the text messages to the NYT, and his office later confirmed their authenticity to NewsNation.

Crooks would have seen the countersniper come out with his rifle, he warned co-workers. The countersniper then told his colleagues that the young man “knows you guys are up there,” The New York Times wrote.

Text messages show law enforcement response

According to the Times, the gunman later moved from the picnic table and was photographed by the countersnipers. Photos of the gunman were shared in a group chat at 5:38 p.m.

“Kid learning around building we are in. AGR I believe it is,” one text read. “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.”

Secret Service agents would ultimately shoot and kill the gunman shortly after he opened fire at 6:11 p.m. Trump suffered a graze to the ear, and one person, former fire chief Corey Comperatore, died in the shooting.

Messages like these could come up during a Senate hearing Tuesday where the acting director of the Secret Service, Ronald Rowe, and deputy director of the FBI, Paul Abbate, are expected to testify. Rowe replaces the former Secret Service director, Kimberly Cheatle, who resigned in the face of bipartisan criticism of the way the Secret Service handled the assassination attempt.

More details on Trump assassination attempt emerge

During a press call Monday morning, FBI officials announced that Trump would be sitting down with officials for an interview at some point. It’s part of standard operating procedures and something that would be done for “any other victim of crime, under any other circumstances,” Kevin Rojek, the special agent in charge of the FBI’s Pittsburgh Field Office, told reporters.

“We want to get his perspective on what he observed,” Rojek said.

To date, the FBI has conducted over 450 interviews, with more likely. Rojek said Crooks’ parents have been “extremely cooperative” with the investigation.

Through the interviews they’ve already done, the FBI said, Crooks has been revealed to be “highly intelligent” but reclusive. Legal requests to view accounts associated with the shooter have been sent to 86 different companies, Rojek said. Crooks, Rojek said, looked online for information about mass shootings and the attempted assassination in May of Slovakia’s populist Prime Minister Robert Fico.

FBI agents have not uncovered a motive for the shooting but believe it was a result of extensive planning, including the purchase of chemical precursors investigators believe were used to create explosive devices found in his car.

NewsNation’s Joe Khalil and The Associated Press contributed to this report.