According to the report, a member of the Beaver County emergency services unit noticed a figure on the roof of the building around 5.45pm local time.

The officer was said to have taken a picture of the person on the building and reported it, but no action was taken.

Video shot prior to the shooting shows onlookers had also spotted the figure on the roof, and attempted to alert police.

An officer from the Butler County Sheriff’s Officer climbed onto the roof and encountered the gunman, but had to retreat when Thomas Crooks pointed his rifle at him.

Crooks opened fire at 6.11pm.

A counter-sniper team was actually inside the building Crooks shot from, the New York Post has reported, quoting unnamed law enforcement sources.

The building was used as a “watch post”, the sources told the Post, but authorities were not on the roof.

It is unknown how Crooks accessed the roof - whether it was from an internal or external stairway.

Meanwhile more detail about Crooks is coming from a bombshell CNN report.

On the morning of the shooting, Crooks bought 50 rounds of ammunition and a short ladder from a Home Depot store, the news outlet reported.

The ladder was apparently used by Crooks to access the roof of the AGR International building, where he fired off eight rounds before he was shot dead by the US Secret Service.

On the day before the shooting, the Friday, Crooks practiced his shooting at the Clairton Sportsmen’s Club where he was a member, CNN quoted an unnamed law enforcement official as saying.

The official also claimed the shooter was carrying a transmitter linked to an improvised explosive device hidden in the trunk of his Hyundai Sonata.

Other reports have stated authorities found two suspect devices in Crooks’ car, and one at his home. All were safely deactivated in the hours after Saturday’s shooting.

The reports come as the FBI said they had gained access to Crooks’ mobile phone, and had completed their search of his home and vehicle. Almost 100 interviews had been conducted so far and the work was continuing, the agency said.

GUNMAN WORE CLOTHES TO BLEND IN WITH ROOFTOP

Former US Secret Service agent Evy Poumpouras said it appeared the shooter took steps to camouflage himself, wearing clothes to blend in with his roof-top sniper position.

Crooks wore a grey T-shirt and pants with a black American flag on his right arm.

She said he used the roof slant to his advantage to set up moments before Trump took to the stage.

The rooftop was about 150m from the Trump stage; for context 150m is a distance at which US Army recruits must hit a human-sized silhouette to qualify using the M16 assault rifle in basic training. The M16 is similar to the AR15 that was used in the shooting.

Ms Poumpourus said she had done many open rally protections and they were always the most difficult as they were “extremely vulnerable” events and were the most anxious for security agents. She described the Secret Service as acting akin to a conductor preparing for a performance, creating the overall plan for inner and outer perimeters then liaising with state and local police.

“You have to think of the secret service like they are the conductor of the orchestra, they create the blueprint and the design for the security plan, they work with state police, they work with local police and then they put in resources and assets,” she told US media.

AD FEATURED TRUMP’S SHOOTER

Donald Trump’s would-be assassin Thomas Matthew Crooks once appeared in an ad for financial giant Blackrock.

In the aftermath of the Trump rally shooting, the financial giant has pulled the ad, The New York Post reports.

The 2022 commercial promotes BlackRock’s pension plans portfolio for America’s public school teachers, focusing on one teacher in particular by the name of Brian De Lallo.

Matthew Crooks graduated from Bethel Park High School the same year the ad was filmed.

“In 2022, we ran an ad featuring a teacher from Bethel Park High School, in which several unpaid students briefly appeared in the background, including Thomas Matthew Crooks,” Blackrock said in a statement to the news outlet.

The company said the ad had been removed from circulation, but was still available for investigators to review, should they so desire.

SHOOTER’S PAST RIFLE SHAME

Armed with America’s rifle of choice, Thomas Crooks blasted his way to infamy, making an unlikely journey from nerdy schoolboy to would-be assassin.

Thomas Matthew Crooks was a bullied loner with few friends, but his attempted assassination of Donald Trump has shocked former school and work colleagues, who saw no hint of extremism in the 20 year old prior to Saturday’s shooting.

Crooks was shot dead by Secret Service agents after he fired six or seven rounds towards the stage when Donald Trump was speaking at the rally in Butler, Pennsylvania. The shots killed 50 year old volunteer firefighter Corey Comperatore and wounded three others, including the former president.

With no manifesto or note yet appearing, a confusing picture is emerging of Crooks’ political beliefs.

But former schoolmates have shed light on the failed assassin’s history with guns.

Crooks had tried out for his high school’s rifle team, but was rejected for being a “terrible” shot, and for making “off-colour” remarks.

Thomas Matthew Crooks, 20, killed a Trump supporter and wounded two others when he opened fire on the Butler Farm Show grounds with an AR-style rifle. The would-be assassin only grazed the former president before being shot dead by the Secret Service.

Two former classmates told the New York Post that the shooting range at the Bethel Park High Schools has seven lanes, each 50 feet long by 21 feet wide.

Crooks once fired from the seventh lane — the closest to the right wall — and hit the left wall, completely missing every target on the back wall. He missed his target by close to 20 feet, former classmate Jameson Murphy recalled.

“He tried out … and was such a comically bad shot, he was unable to make the team and left after the first day,” Murphy said.

Crooks — who has been described as a loner who wore hunting outfits to class “couldn’t shoot at all. He was a terrible shot,” a second classmate added.

Even the coach, they continued, had concerns about Crooks.

“Our old coach was a stickler, he trained Navy marksmen, so he knew people. He knew when someone’s not the greatest person,” the ex-classmate explained.

INVESTIGATORS GRILL NEIGHBOURS

Federal agents are still searching for a motive, days after Thomas Matthew Crooks shot and wounded Donald Trump in an assassination attempt.

Agents wearing shirts emblazoned with “Pittsburgh Bureau of Federal Investigation” spent the morning speaking to the Crooks and their neighbours, brandishing their badges at the front door.

“They asked questions I didn’t really have answers to. I’m not really one to go around talking to my neighbours,” said Kelly Little, 38, who has lived across the street from the Crooks’ modest one-story brick house since 2018.

“They asked if I knew them or if I’d seen anything out of the ordinary. I didn’t have any great answers for them.”

While speaking to agents, Little said she learned for the first time of the existence of Crooks’ older sister, Katherine. “I had no idea she existed.”

GUNMAN BOUGHT 50 ROUNDS OF AMMO BEFORE SHOOTING

Crooks bought 50 rounds of ammunition at a local gun store hours before opening fire at Donald Trump, a senior law enforcement source told CNN.

From the roof of a manufacturing plant about 130 yards away from Trump’s rally, he fired eight rounds of ammunition before Secret Service snipers responded, killing Crooks instantly.

He was found with an AR-style semi-automatic assault rifle that his father had bought and was wearing a shirt for a popular gun YouTube channel, Demolition Ranch.

POLITICAL ALLEGIANCES UNCLEAR

Crooks made a $US15 donation to a Democrat voter turnout group on January 20, 2021 – the day Joe Biden was inaugurated as America’s 46th president.

But in September that year Crooks registered to vote as a Republican in Allegheny County, the municipality including Bethel Park, the Pittsburgh suburb where he lived with his parents.

CNN reported that both parents are social workers, his mother a registered Democrat and his father Matthew a registered Libertarian.

It is believed the AR-15 rifle Crooks used in the assassination attempt belonged to his father, which he reportedly purchased from a gun shop in Bethel Park.

‘HE WAS BULLIED EVERY DAY’

How Crooks went from being a nerdy computer-game playing teen with a penchant for wearing hunting gear to school, to being the perpetrator of one of America’s worst acts of political violence, is unclear.

Former students at Bethel Park High School, which Crooks attended before graduating in July 2022, told US media outlets that “Tom” was a smart but quiet loner who was frequently bullied.

“He never outwardly spoke about his political views or how much he hated Trump or anything. (He had) few friends,” former classmate Sarah D’Angelo told the Wall Street Journal.

Another former classmate, Jason Kohler, remembered him as being “bullied every day” for wearing camouflage gear, while a passenger on his school bus, Abdulloh Rakhmatoz, said: “(He was) very quiet but when he did talk he was nice. He was just really shy.”

Crooks had been working as a dietary assistant at Bethel Park Skilled Nursing and Rehabilitation Center since graduating from school, earning around $US16 ($A23.60) per hour.

Marcie Grimm, the administrator at the facility, said he “performed his job without concern and his background check was clean”.

An employee at the centre who spoke to CNN on condition of anonymity described him as “a friendly face in the hallway”.

A CLEAN HISTORY

The apparent disconnect between Crooks’ previous behaviour and the act of political violence that has up-ended the campaign for the US presidency will pose a problem for investigators as they try to ascertain his motive.

Police said Crooks had no history of mental illness and no criminal convictions; nor was there any evidence of disturbing social media posts.

And yet there he was, armed with a rifle, crawling along the roof of a manufacturing warehouse belonging to AGR International, some 140 metres away from the Butler Farm Show Grounds, where Trump was speaking. He was dressed in a T-shirt that advertised a YouTube channel called Demolition Ranch which focuses on guns and explosives.

Authorities later found a “suspicious device” in Crooks’ vehicle which was rendered safe by bomb disposal experts.

Footage circulating on social media taken just before the shooting shows onlookers clearly alarmed by the presence of the armed man on the roof, as tried to alert police to his presence.

One officer from the Butler County Sheriff’s office climbed the roof and encountered Crooks, but had to back down the ladder when the young man pointed his rifle at him.

Seconds later, he fired off his first shots.

WHAT THE SHOOTING TELLS US

Crooks showed a reckless disregard towards the spectators he fired upon at Donald Trump’s rally in Pennsylvania, and was likely unconcerned about his own survival, an expert on sniper shootings suggested.

A highly-trained but now retired NSW Police marksman, who prefers to go by his nickname Fingers, said “competent snipers” plan an escape route to ensure their survival, but it appeared Crooks had not done this.

“If you don’t care about your own survival you take the consequences,” he said.

“He was happy to be exposed, during and after the event. Once the first rounds were fired, his position was given away,” Fingers said.

The NSW police veteran said the AR-15 rifle Crooks used would have weighed about four kilograms and its length could be between 30-40 inches (76-101cm) depending on the barrel, although some can be shorter.

“It’s a fairly comfortable weapon but not concealable; he couldn’t conceal it wearing clothes,” Fingers said.

“It will be interesting to know if he accessed the roof through an internal or external stair.”

Crooks’ shooting experience would have been just one factor in determining his ability to hit a target from up to 150 metres away, Fingers said. The weather conditions, the optics on the weapon and how well it was maintained would all play a role on the shooter’s accuracy.

The fact Crooks fired off about six or seven rounds was also indicative of his headspace, Fingers suggested.

“He wasn’t concerned about missed rounds striking the audience,” he said.

While a ballistics report has not yet been prepared, Fingers said it was possible Trump’s ear injury was caused by a ricocheting fragment rather than an actual bullet.