New footage appears to show would-be Donald Trump assassin Thomas Matthew Crooks lurking in the background of the rally ... an hour before he shot at the former president.
In video recorded by a man who attended Saturday's rally, you can see a person matching Crooks' description -- and he's pacing around the event's perimeter, just on the outskirts of the main event ... right by the building Crooks climbed an hour later to take aim at Trump.
The footage was obtained by WTAE-TV Pittsburgh ... and the Trump supporter who filmed it says when he looked over his footage and noticed Crooks in the background, he couldn't sleep ... let alone believe he'd captured the shooter inadvertently.
The cameraman explains he was trying to capture the size of Trump's crowd when he whipped out his phone and recorded the scene ... and the footage also shows some of the police presence in Butler, with cops not far from where Crooks was walking around.
About an hour after the video was recorded, Crooks climbed onto the roof of a nearby building and took a shot at Trump with an AR-15-style rifle before being killed by return fire from snipers.
Crooks' parents reported him missing on the day of the rally ... and he reportedly took Saturday off work and told coworkers he would be back Sunday.
Security personnel were said to be keeping an eye on Crooks at the rally ... he first raised suspicions 3 hours before the shooting when he brought a rangefinder through a security screening checkpoint.
Now, he's on video seemingly casing the place an hour before the assassination attempt. The more that comes out -- the more it seems this dude stuck out like a sore thumb that day.