Thomas Crooks spotted on roof by Secret Service 10 minutes BEFORE Donald Trump took stage at Pennsylvania rally, sources say

Members of Congress learned that the would-be Donald Trump assassin Thomas Crooks was spotted by Secret Service 10 minutes before he walked out onstage, and 20 minutes before he was shot.

On Saturday, 20-year-old Crooks shot multiple rounds at Trump, clipping his ear, injuring multiple attendees and tragically killing former firefighter Corey Comperatore. 

After waiting days to learn more of the assassination attempt, lawmakers were briefed by the FBI and Secret Service Wednesday on key details about the ongoing investigation. 

Sources on the call told DailyMail.com that over an hour passed from the shooter being spotted to his initial shot. Even more troubling, Secret Service counter snipers saw Crooks on the roof 20 minutes before he shot the former president.

At 5:52 p.m. the 'suspicious' shooter was spotted on the roof by counter snipers. 

Trump walked out onto the stage at 6:02 p.m. 

Then at around 6:12 p.m. Crooks' first shots rang out.  

'That is a crazy amount of time they let pass before firing,' the source said. 

Sen. Mike Lee, R-Utah, confirmed this in a tweet Wednesday afternoon.

'They had identified the shooter as 'suspicious' a full 19 minutes before the shooting,' he posted. 

Lee said that senators were only allowed to ask four questions during the briefing, which he described as 'arbitrarily cut the call short.' 

Adding insult to actual injury, the officials in the briefing did not provide any information about why their response took so long. 

Secret Service Director Kimberly Cheatle did not know how Crooks got onto the roof, the source added. 

Also coming into question on the call was the possible motive for Crooks to commit such an atrocity. 

Officials did not confirm an operating motive and said that his rationale remains a mystery.  

They said that they have yet to find any ideological material that could shine light on why Crooks decided to shoot the former president.

But, they did reveal that Crooks operated several accounts on encrypted platforms that they are still working to gain access to, the source said. 

'He was identified as a character of suspicion because [he had] a rangefinder as well as a backpack. And this was over an hour before the shooting actually occurred,' Sen. John Barrasso, R-Wyo., said on Fox News Wednesday afternoon.

'So, you would think over the course of that hour, you shouldn't lose sight of the individual.'

'Somebody ought to be following up on those sorts of things. No evidence of that happening at all.'

The Wyoming Republican later posted a statement calling the meeting a '100 percent cover-your-a** briefing.'  

Secret Service Director Kimberly Cheatle has said the agency's performance at the rally was 'unacceptable,' Tuesday evening, but previously she had sought to shift blame on others. 

Shortly after the shooting she noted how local authorities were in charge of securing the building Crooks was on. 

Later, she walked that back Tuesday and said the Secret Service was 'solely responsible' for not preventing the attack.

There are multiple investigations into the shooting from both within the Department of Homeland Security (DHS) - the agency that oversees the Secret Service - and in Congress. 

Cheatle is expected to testify about the shooting on Monday before the House Oversight Committee.