Latest developments in the investigation

BUTLER, Pennsylvania – Investigators are searching for clues as to what may have driven Thomas Matthew Crooks to try to assassinate former President Donald Trump at a rally in Pennsylvania.

The 20-year-old first came to officers’ attention at Saturday’s rally when onlookers noticed him acting strangely outside the campaign rally. The tip-off sparked a frantic manhunt, but officers were unable to find him before he made it to a rooftop, where he opened fire and was then shot and killed by Secret Service snipers.

3 snipers were in the shooter’s building

CBS News learned that three government snipers were stationed in the building used by the shooter.

The plan was for them to stay inside the building and face the rally. The information was first reported by BeaverCountian.com.

One of the snipers inside saw Crooks outside looking at the roof and the rest of the building and disappearing, a local police official told CBS News. Crooks came back, sat down and looked at his phone.

One of the snipers took a photo of Crooks.

Crooks pulled out a rangefinder and the sniper alerted the commanders. Crooks walked away and came back with a backpack. The snipers relayed this information and said he went to the back of the building.

Officials believe he may have used an air conditioning unit to get onto the roof.

He was already on the roof when other officers arrived for backup. State police rushed to the scene, but Crooks had already been shot by the time they arrived.

Further new details of the investigation:

• According to a police bulletin obtained by CBS News, the crooks purchased 50 rounds of ammunition at a gun store in Bethel Park before the rally.
• Two law enforcement officials familiar with the investigation told CBS News that the gunman visited a shooting range in the days before the shooting.
• The AR rifle used by Crooks was purchased legally in 2013, two sources confirmed to CBS News. It was previously reported that it was purchased by the shooter’s father.
• After the shooting, investigators found three suspected explosive devices, two of them in the shooter’s vehicle, which was parked near the rally site.
• CBS News reported that three law enforcement officials said the shooter’s father called police after the shooting. The exact reason and timing of the call are unknown. The FBI says the family is cooperating with investigators.
• Investigators have gained access to the shooter’s phone but have not yet been able to provide any important information.

The FBI conducted nearly 100 interviews with police officers, rally attendees and other witnesses and received hundreds of tips from digital media.

The FBI said it is investigating the attack as a possible act of domestic terrorism, but could not identify a clear ideological motive. The FBI believes Crooks acted alone.

Strange behavior outside the event

Officials say law enforcement became aware of Crooks when spectators at the Trump rally noticed him acting strangely outside the event.

Police had a report of a suspicious man pacing near the magnetometers and apparently exchanging photos of the suspect. Witnesses pointed to an armed man on a nearby roof and shouted at him.

When a police officer climbed onto the roof to investigate, the shooter turned and pointed his rifle at him. But the officer didn’t fire a single shot – or couldn’t.

Butler Township Administrator Tom Knights said the officer lost his footing and did not back away as he fell 8 feet to the ground.

“He was literally dangling off the edge of a building, assuming the defensive position he needed to assume at that point. He couldn’t hold himself upright,” Knights said.

The crooks fired six to eight shots at Trump after he fell to the ground.

A sniper took Crooks down within seconds of him firing the AR rifle, but it was too late.

Former Secret Service agent angry about security breach

Ron Layton, a former Secret Service agent, told CBS Pittsburgh that he and other police officers were “angry” about the lack of protection that led to the shooting.

“The people who worked in the Secret Service and who are on active duty are angry. We are angry. I am angry,” Layton said.

“He shouldn’t have access to the roof. That’s his job, that’s why the building is occupied. So this should never have happened.”

Sheriff says construction is “not our responsibility”

Andy Sheehan, a reporter for CBS Pittsburgh’s KDKA-TV, interviewed Butler County Sheriff Michael Slupe about communications with the Secret Service regarding securing the building.

“I can’t comment on that because, you know, as far as the building goes, I don’t know because it wasn’t our responsibility, but they had a very good briefing,” Slupe told KDKA-TV. “And like I said, at some point you get a briefing and you recognize, adapt and overcome the situation. And there are a lot of well-trained police officers who are absolutely capable of doing that.”

Slupe said he had “no idea” about plans to secure the building.

“No, the sheriff’s office was not asked to do this, and I don’t know who would have been responsible if that had been part of their plan,” he said.