Trump shooter Thomas Matthew Crooks is seen dead on the roof in chilling new video confirming Secret Service was warned

Dramatic new footage shows law enforcement standing over the dead body of Donald Trump's attempted assassin moments after he was killed.

A Secret Service agent and local police are seen in the video discussing how Thomas Matthew Crooks had been identified as a suspicious person before he started shooting.

The graphic clip shows a pool of blood trailing out from the 20-year-old's body, which lies next to the rifle he used during the shooting.

'So this is the guy,' the Secret Service agent says to a Beaver County Emergency Service Unit officer, confirming they were aware of the threat and raising questions over their handling of the incident.

Dramatic new footage shows law enforcement standing over the dead body of Donald Trump 's attempted assassin moments after he was shot dead

The bodycam footage was released by Iowa Sen. Chuck Grassley and shows the moments after the shooting, which left Trump injured and killed firefighter Corey Comperatore, 50.

Crooks opened fire as the presidential hopeful was delivering a speech at a rally in Butler, Pennsylvania last week.

The clip shows Crooks lying lifelessly on top of the roof he scaled in order to take the shot.

In the video, the Secret Service agent is informed that Crooks had been spotted by a sniper, who sent his picture out to other law enforcement officers.

They then begin discussing his bike which has been spotted nearby. 

'So we're treating that as suspicious device?' the Secret Service agent confirms.

The camera then pans to reveal the rifle Crooks used in the shooting and they confirm he is the same person as in the images taken by the sniper which they say  feature Crooks wearing his distinctive glasses.

Thomas Matthew Crooks opened fire on Donald Trump as he was speaking at a political rally in Butler, Pennsylvania

The graphic video shows Crooks' lifeless body lying next to his rifle in a pool of blood as a Secret Service agent discusses how they had been aware of him as a 'suspicious' person before he opened fire

The backpack affixed to this bicycle was reportedly related to Crooks' assassination attempt. In the video, local police confirm that the bike is being treated as a 'suspicious device'

The Secret Service agent also states that people who had been filming in the moments leading up have also been detained.

'Maybe they were involved, maybe they weren't. The guys that saw them said, "they were filming us, then filming the guy on the roof, then filming us".' he says.

'When the shots started firing they tried to run away, isn't that what everyone would do that had a phone? I'm not saying they were involved or they weren't involved but I got no problem detaining them.

'I just want to detain those guys find out what they know, who they are whatever, I'm trying to get clear information to relay back to DC.'

Crooks was captured in a chilling video lurking near the former president's rally stage just an hour before he unleashed a hail of bullets.

The disturbing footage, shot by someone in the crowd, appears to show the gunman stalking around a building he would climb 60 minutes later in order to get the perfect vantage point from which to target Trump.

The footage was revealed amid a series of stunning developments that have raised more questions about the massive security failure that led to the attempt on Trump's life.

Police told the Secret Service agent that a sniper spotted Crooks and sent his picture around law enforcement officers

The video shows local police and a Secret Service agent discussing how Thomas Matthew Crooks had been identified as a suspicious person before he started shooting

It emerged the gunman's' father called police on the day of the shooting because Crooks didn't return from what he thought was a routine Saturday trip to the local gun range.

And it was revealed Crooks was at the former president's rally three hours before opening fire, even sparking the suspicions of the Secret Service during that time because he was carrying a rangefinder used by hunters to take long shots.

But he was never stopped or questioned.

He later climbed onto the roof of the building he was lurking near, shot Trump and killed retired volunteer fire chief Corey Comperatore.

Crooks had told his boss he needed the day off from work Saturday and gave colleagues a final chilling message: That he would be back on Sunday.

Witnesses spotted Crooks crawling onto the roof of the American Glass Research building.

The last photo of would-be Trump assassin, Thomas Crooks, 20, showing him clad in a t-shirt branded with the logo of YouTube channel Demolition Ranch 

 A Secret Service counter-sniper team codenamed 'Hawkeye' also spotted him looking at their position through the rangefinder.

The Clairton Sportsmen's Club where Crooks' father believed him to be heading around 1 pm states on its web site that its high-power rifle range 'has 10 firing benches with targets at 50, 100 and 187 yards.'

Crooks is believed to have been firing from about 165 yards when his bullet struck Trump in the right ear after the former president turned to read from a stats screen.

On Tuesday, embattled Secret Service Director Kimberly Cheatle dramatically announced Tuesday her resignation in the wake of the colossal security failures that led to Trump being shot.

Cheatle took responsibility for the catastrophic lapses after she was lambasted by Republicans and Democrats alike when she appeared before Congress on Monday.

The security chief had faced mounting questions over why an agent was not stationed on the roof from where the gunman opened fire on the former president, and why Trump was allowed to take the stage even when a threat was detected.