The footage, obtained by Fox News, shot from the bleachers behind Trump, shows Crooks moving quickly along the roof of the American Glass Research Building, disappearing and then popping back up ... minutes before squeezing off 8 shots.

It's the first video showing Crooks and Trump in the same frame ... and this new vantage point illustrates just how close the rooftop was to where Trump was on stage.

This video was reportedly recorded at 6:08 PM ... a full 3 minutes before Crooks opened fire with his AR-15-style rifle. You see Trump speaking at the podium, plus the large crowd and the building in the background, with Crooks shuffling along the top of the building.

How did law enforcement not notice Crooks, and take steps to protect Trump?!?

James Copenhaver filmed the video, and he's one of the two victims who were struck by gunfire and critically wounded during the July 13 Trump campaign rally in Butler, PA.

Crooks hit Trump in the ear with one shot, but fired the rest of his shots into the crowd ... killing Corey Comperatore and injuring Copenhaver and David Dutch.

Other videos from rallygoers show Crooks hanging out along the base of the building during the rally ... and the FBI says he flew a drone over the farm grounds earlier in the day, before law enforcement flagged him as a "suspicious person."

Remember ... video shows Crooks pulling himself onto the roof at 6:06 PM and he was then spotted by law enforcement and spectators two minutes later, when this new video was shot.

The FBI says a cop was hoisted onto the roof at 6:11 PM ... Crooks confronted him with a rifle and the cop dropped to the ground and radioed in that Crooks was strapped with a "long gun."

Incredibly, the Secret Service still allowed Trump to continue speaking ... and Crooks was able to fire off 8 rounds.