Three law enforcement countersnipers were posted inside the building that suspected gunman Thomas Matthew Crooks climbed up to open fire upon former President Donald Trump during a campaign rally in Pennsylvania on Saturday.

What’s more, the law enforcement snipers noticed Crooks walk up to the building and look at its roof, according to a local law enforcement source who spoke with CBS News.

Crooks walked away but quickly returned, when one of the law enforcement snipers took a photo of him, the source said. The sniper called the command post about Crooks after he pulled out a range finder to determine a target’s distance.

The 20-year-old gunman walked out of sight again and returned with a backpack. The law enforcement source said the snipers radioed for backup and told command that Crooks was walking toward the rear of the building, which was more than 150 yards from the rally stage.

Minutes later, Crooks fired eight rounds at the stage, killing one man, wounding two other people and grazing Mr. Trump’s right ear. Countersnipers positioned near the stage shot and killed Crooks shortly afterward.

Bystanders also called out to police about Crooks’ behavior before the first shot was fired.

Multiple people reported a suspicious man pacing near the rally’s metal detectors, prompting a response from two Butler Township police officers, according to a law enforcement source who spoke with The Associated Press.

One of the officers hoisted the other so he could scan the building’s roof. When Crooks noticed the officer, he turned around and pointed his gun at the cop. 

Butler Township Manager Tom Knights said the officer lost his grip and fell 8 feet to the ground, injuring his ankle. 

“He was literally dangling from the edge of a building and took the defensive position he needed to at that time. He couldn’t hold himself up,” Mr. Knights told the AP.

Butler County Sheriff Michael Slupe also defended the officer’s reaction, saying the lawman couldn’t grab ahold of his gun in that situation.

“I think all law enforcement on site did everything that they could, especially the local law enforcement,” Sheriff Slupe told the AP. “I hope they’re not made a scapegoat, because they did their job to the best of their abilities.”

Rally security included the Secret Service, Pennsylvania State Police and about a dozen local police officers and sheriff’s deputies.

Secret Service Director Kimberly Cheatle told ABC News on Monday that local police were inside the building while the gunman was on the roof. 

She also said local authorities were responsible for securing the building.

“In this particular instance, we did share support for that particular site and that the Secret Service was responsible for the inner perimeter,” Ms. Cheatle said. “And then we sought assistance from our local counterparts for the outer perimeter. There was local police in that building — there was local police in the area that were responsible for the outer perimeter of the building.”

Sheriff Slupe said in a separate interview that securing the building wasn’t his department’s responsibility. 

Ms. Cheatle, who took over the agency’s top job in 2022, said she wouldn’t step down from her role despite the failure.

She is expected to testify about the assassination attempt before the House Oversight Committee next week.

• This article is based in part on wire service reports.

• Matt Delaney can be reached at mdelaney@washingtontimes.com.