CNN  — 

Investigators believe the gunman who attempted to assassinate former President Donald Trump may have used a drone on a reconnaissance trip to the rally site on the day of the shooting, a law enforcement official familiar with the investigation told CNN.

Investigators searching Thomas Crooks’ belongings found a drone in his car. The working theory investigators are exploring is that the drone would have given Crooks an overview of the rooftops of nearby buildings and how they connect, according to the law enforcement official. That could have helped him choose the spot where he fired the shots toward the podium where Trump was standing.

New evidence shared by multiple law enforcement officials also reveals that a ladder purchased by Crooks several hours before he opened fire and a backpack believed to have belonged to him have been located and are in the possession of federal authorities.

A man driving near the shooter’s home discovered the ladder and backpack on the side of the road, according to law enforcement sources from two separate agencies. The person reportedly saw the ladder in that location for several days before deciding to alert authorities.

The discoveries of the ladder, backpack and drone come as investigators are struggling to find a motive for Crooks’ assault. As more details are released about the failed assassination attempt, the US Secret Service has faced questions and criticism and is scrambling to?increase security?ahead of the first campaign rally with both Trump and Republican vice presidential nominee Sen. JD Vance on Saturday.

As the investigation continues, authorities are likely to scrutinize these newly found items for any clues that might help piece together the sequence of events before last Saturday’s shooting.

Investigators have looked into what Crooks was doing in the days and hours leading up to his attempt to assassinate the former president, including combing through his physical and digital trail. After the shooting, multiple law enforcement sources said investigators found a bulletproof vest, three fully loaded magazines and two remote-controlled explosive devices in Crooks’ car.

Additionally, after a search of his residence, investigators discovered another bulletproof vest, another remote-controlled explosive device and a 3D printer, according to multiple law enforcement sources.

The suspect’s cell phone contained images of both Trump and President Joe Biden, and his search history included dates of the Democratic National Convention as well as future Trump events. Along with images of Trump and Biden, the shooter’s phone also contained pictures of congressional leaders, such as House Speaker Mike Johnson and House Minority Leader Hakeem Jeffries.

Crooks had?searched for information?on another recent mass shooter who shot and killed four classmates at a Michigan high school in 2021. The web searches about that shooter, Ethan Crumbley, are consistent with what law enforcement officials have seen in other mass shooters who research people they wish to emulate.

The suspect?would have been at work?on the day of the attempted assassination, but he told his boss he needed the day off because he had?“something?to do” and told his co-workers he would be back to work on Sunday.

As the investigation remains in its early stages, federal investigators have pieced together?an early portrait of Crooks?as an intelligent, unassuming loner who expressed an interest in guns and was far from outspoken about politics.