Shocking new details reveal how Trump shooter evaded Secret Service and cops THREE times - with one agent even taking a photo of him - before opening fire from top of building with counter-sniper team inside

A team of police snipers team saw Thomas Crooks scouting their command post three times in the minutes before he climbed on top of it and shot Donald Trump from just inches above their heads, it has emerged.

Three police marksmen from Beaver County were using the single-story AGR International building as their watch-post when the would-be assassin chose it as his place to shoot from, CBS reported.

And he may have been in place on the roof for up to 30 minutes before he unleashed his volley of shots that killed one man and nearly took the life of the 45th president on Saturday evening.

A law enforcement official told the channel said that no action was taken after one of the snipers first spotted Crooks looking up at the roof of the building in Butler, Pennsylvania, just 130 yards from where the president would speak.

The 20-year-old disappeared around a corner before he was seen a second time, sitting down and looking at his phone, prompting one of the snipers to take his picture.

Thomas Crooks was shot dead by Secret Service officers on the roof of the police look-out just 130 yards from where former President Donald Trump was speaking on Saturday evening

The 20-year-old would-be assassin was repeatedly seen and photographed by police officers before scaling their building and opening fire 

The sniper then radioed to a command post after seeing Crooks take out a rangefinder.

But no further action was taken before Crooks reappeared a third time, this time wearing a backpack and disappearing from sight as he walked to the back of the building.

A further radio report relaying the information was submitted by the sniper team who did not realize that Crooks was now scaling their building.

Eight members of the Beaver County Police Department had been tasked with securing the outer perimeter of the rally, while the Secret Service concentrated on the rally itself.

Pittsburgh's WPXI reported that a Beaver officer took a photo after seeing Crooks on the roof at 5.45pm, by which time he had already been photographed on the ground by a colleague.

The final radio report by the three-strong sniper team prompted State police to send reinforcements to the building but it was not until 6.11pm that one climbed onto the roof and saw Crooks with his rifle.

The officer from Butler County was forced to retreat when Crooks aimed his AR-style weapon at him, and it was seconds later that the killer unleashed up to eight shots, killing Pennsylvania fire chief Corey Comperatore, critically injuring two others and hitting Trump in the right ear.

It is not clear whether Crooks had the rifle on him when he was first seen outside the AGR International factory building, or if he stayed on the roof for the whole time.

A member of the public is seen talking with a police officer before the shots rang out, the building where Crooks was perched is to the right 

Trump grabbed his right ear as the first shots rang out at 6:12pm 

As Trump pumped his fist to the crowd, some were heard cheering his name and chanting 'USA' and 'Make America Great Again' 

But the shocking new allegations surfaced as authorities and the US Secret Service face mounting questions over how Crooks was able to shoot the former president and kill a member of the rally crowd. 

A horrifying video shows witnesses pointing at the roof and shouting at officers trying to warn them. MAGA fans also say they alerted law enforcement to Crooks as he crawled to his shooting position, but he was still able to shoot.

Law enforcement at the event in Butler, Pennsylvania are facing intense scrutiny after it was revealed the roof was flagged as a security 'vulnerability'.

Secret Service Director Kimberly Cheatle said on Monday night that she would not resign despite mounting calls for her to step aside over the huge lapses that led to one of the most horrific acts of political violence in history.

The local Pennsylvania sheriff defended the police officer who confronted Crooks on the roof seconds before the shooting.

Butler County Sheriff Michael Slupe confirmed on Monday that one of his armed officers encountered the gunman on the roof just before he unleashed carnage on the former president's rally.

Slupe defended his officer's decision to retreat, telling KDKA he would 'have done the same thing.'

'All I know is the officer had both hands on the roof to get up on the roof, never made it because the shooter had turned towards the officer, and rightfully and smartly, the officer let go,' Slupe added.

'I mean, people think the officers are supermen like you hold on the roof with one hand while you are hanging on for dear life and pull a gun out. It doesn't work that way.

Slupe also said that members of his department were alerted to Crooks' suspicious behavior before the rally began and started searching for him right away.

Local police, not the Secret Service, swept the building, but Crooks was still able to climb to the top and take aim at the former president.

Slupe acknowledged that Crooks was in the 'secondary ring' of protection when he opened fire.

He said the Secret Service is responsible for the ring immediately around the president, but local police take control of the outer ring.

Butler County Sheriff Michael Slupe insisted his officer was right to retreat after would-be assassin Thomas Crooks pointed a rifle at him just seconds before the fatal shots were fired 

Attendees claimed they warned the Secret Service after seeing a man on the roof where the gunman was later killed 

The former president, 78, survived the horrifying assassination attempt when the bullet missed him by less than an inch on Saturday afternoon.

It came eight minutes after he took the stage at 6.03pm ET, where Trump began his remarks and pointed to a large graphic in the same direction where the shooter was perched atop an AGR International building.

Even before he took the stage, Trump supporters said they spotted the gunman 'bear-crawling' across the roof with a rifle, but claimed their warnings to Secret Service were ignored.

'I'm thinking to myself 'Why is Trump still speaking, why have they not pulled him off the stage,''' one witness told the BBC. 'The next thing you know, five shots ring out.'

With the sun still high on a bright day, Trump emerged to 'God Bless the USA' playing over the loudspeakers at 6.03pm, and remained waving and shaking his fist at the crowd for several minutes.

Trump brought out a large graphic with statistics on the migrant crisis at the southern border, and told the crowd at 6.11pm: 'That chart's a couple of months old...'

'If you want to really see something that's sad, take a look at what happened,' Trump continued - before he abruptly grabbed the side of his head as several 'pops' filled the event space.

The 78-year-old dropped to the floor in an instant as five more shots rang overhead in quick succession, before four Secret Service agents raced to the stage and dove on top of the former president.

Stunning images showed Trump cowered on the floor as agents protected him, with blood dripping down his cheek.

A timeline showing the dramatic events that took place on July 13

Several more Secret Service agents continued to flood the stage, while four heavily armed officers lined the perimeter ordering attendees to 'get down.'

The sniper, sat 400ft across from the rally on an exposed rooftop, fired another shot at the stage a second later while Trump fans streamed out of the bleachers.

Secret Service officers scrambled to take control of the pandemonium, and surrounded the injured ex-president before getting him off stage.

Officers shot Crooks dead.