Shocking security lapses by the U.S. Secret Service and local police are emerging as more is learned about the movements of the man who tried to assassinate Donald Trump during a campaign rally in Pennsylvania on Saturday.

Officials have already acknowledged there was no security on the roof where the gunman opened fire, allowing him to get very close to the former president.

But new reporting shows that authorities had been tracking him before the shooting.

Here is what we know.

A young man acting strangely

Thomas Matthew Crooks was on the radar of security officers at a campaign rally in Butler, Pa., at least an hour before firing gunshots at Trump, FBI officials said during a briefing on the shooting.

Thomas Matthew Crooks is shown in his 2021 Bethel Park High School yearbook photo.

(Bethel Park School District)

A local law enforcement officer noticed the 20-year-old acting strangely outside the rally venue, officials said. Attendees saw Crooks pacing near magnetometers at the event entrance, according to reporting from the Associated Press.

Local officers alerted their command post and snapped a photograph of him, and radio communications alerted the Secret Service of his presence, law enforcement sources told The Times.

But authorities soon lost sight of Crooks as they monitored the thousands of other people at the Butler Farm Show, the sources said.

Suspicions before Trump’s speech

About 20 minutes before Trump took the stage, a local police officer in a surveillance position saw Crooks near a building beyond the area secured by the Secret Service, according to Republican U.S. senators who received briefings on the matter.

Attendees also noticed Crooks, who had climbed atop the roof with an AR-style rifle. In multiple videos from the rally shared on social media, people can be heard shouting, “He’s got a gun!” as they point to where Crooks was positioned.

Local officers tried to climb up to the roof but were deterred when the gunman pointed his weapon at them, sending them ducking for cover, Butler County Sheriff Michael Slupe told local news stations.

According to Sen. John Barrasso (R-Wyo.), who was at a Wednesday briefing by the FBI and Secret Service, Crooks had a backpack and a range finder, a binocular-like device used to pinpoint the distance to a target.

Republican presidential candidate Donald Trump arrives for the campaign rally in Butler, Pa., on Saturday.

(Evan Vucci / Associated Press)

Trump speaks, despite security threat

Despite all of the information about a potential threat, the Secret Service chose not to cancel Trump’s speech.

Trump took the stage at 6:02 p.m. About six minutes later, attendees spotted an armed man lying on the back side of the American Glass Research roof, a little over a football field from Trump’s stage. Video showed onlookers pointing up and expressing their concern.

The building was meant to be covered by local law enforcement because it was not in the immediate vicinity of the venue, which was secured by the Secret Service, according to law enforcement sources not authorized to speak publicly about the investigation.

A shocking discovery on the roof

Two officers set out to check the American Glass Research rooftop, with one boosting the other up to peer over the edge. According to a Facebook post from Butler Township Commissioner Edward Natali, Crooks turned his firearm toward the officer, who immediately ducked and fell back, injuring himself.

Knowing he had been discovered, Crooks then crawled to the roof’s peak and aimed at Trump. About 6:11 p.m., he fired eight shots, killing former local fire chief Corey Comperatore, wounding two others and clipping Trump’s ear with a round. Within 10 seconds of the first shot, Secret Service snipers fired on Crooks and killed him.

Experts have told The Times the delay from the snipers occurred because they were trying to locate the gunman’s position. The pitched roof where Crooks was positioned seemingly made it difficult for snipers to see him.

Internet searches for Biden and Trump

It isn’t clear how long Crooks had been planning the shooting. He conducted internet searches for appearances by both Trump and President Biden before seemingly settling on the Butler location 50 miles from his home in Bethel Park, Pa., law enforcement sources told The Times.

On the morning of the shooting, he bought a ladder and 50 rounds of ammunition and practiced at a gun club, according to law enforcement sources. After he was killed, agents found homemade explosives inside his car and a remote detonator alongside his body, according to those familiar with evidence gathered in the investigation.

Republican presidential candidate Donald Trump is helped off the stage following the assassination attempt in Butler, Pa.

(Gene J. Puskar / Associated Press)

Pointing fingers

U.S. Secret Service Director Kimberly Cheatle said in an interview with ABC News that no one was guarding the roof of the American Glass Research building because its pitch was considered unsafe. She said local police were responsible for the outer perimeter of the building.

But Butler County Dist. Atty. Richard Goldinger told the Washington Post that the Secret Service “was informed that the local police department did not have manpower to assist with securing that building.”

Natali said on Facebook that seven local officers had been assigned to traffic detail in the area and some left their posts to help search after hearing reports about a suspicious man — including one who tried to climb onto the roof.

He said anyone saying local police were assigned to that building was “lying or covering their backsides.”

On Wednesday, Cheatle was subpoenaed by the House Oversight Committee, which labeled the attempted assassination “a total failure of the agency’s core mission.”