Secret Service Head: Cops Were In Building While Trump Shooter Was On Roof

United States Secret Service Director Kimberly Cheatle provided new details about the assassination attempt on Donald Trump during an interview with ABC News .

Cheatle told ABC News Chief Justice Correspondent Pierre Thomas that authorities had identified the shooter, Thomas Matthew Crooks , as a "potential person of suspicion" before he opened fire on Trump while he was speaking at a campaign rally in Butler, Pennsylvania, on Saturday (July 13).

"I don't have all the details yet, but it was a very short period of time," she said. "Seeking that person out, finding them, identifying them, and eventually neutralizing them took place in a very short period of time, and it makes it very difficult."

According to a report by Fox News , a local law enforcement officer noticed a man carrying a range-finder about 30 minutes before the assassination attempt. He contacted the Pennsylvania State Police to report what he saw, and they discussed whether the man was carrying binoculars so he could see Trump better.

Cheatle said that agents identified the one-story building where Crooks was perched as a potential security concern before the rally and tasked the local police with securing it .

"In this particular instance, we did share support for that particular site and that the Secret Service was responsible for the inner perimeter," 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."

However, Cheatle, who has resisted calls to resign, took full responsibility for the failure that allowed the shooter to open fire on the former president.

"The buck stops with me," she said. "I am the director of the Secret Service, and I need to make sure that we are performing a review and that we are giving resources to our personnel as necessary."