Notice the first paragraph,He didnt have a weapon on him when he went through security gate. Only the rangefinder.
"Crooks reportedly was placed on the radar of security when he went through the metal detector screening area with a rangefinder, which is used by shooters to measure distance. He did not have a weapon on him at the time, though he was flagged to keep an eye on. At some point, he left the secure area and didn’t pop up again until rally attendees were trying to bring attention to an armed person crawling on the nearby rooftop.
Around the time that Crooks was spotted by witnesses on the roof, a counter-sniper team spotted Crooks taking out the rangefinder and looking at counter-sniper positions, a senior law enforcement official told the outlet. "They were looking at him while he was looking at them," the official said. Crooks reportedly gained access to the rooftop by climbing on top of the building's air conditioning unit and pulling himself up.
After Crooks was neutralized following his attempted assassination of
Trump, remote detonators were reportedly found on Crooks’ body that went to remote-controlled bombs found in Crooks’ car. An explosive device was also found at Crooks' residence. Sources said that Crooks was found with three loaded magazines and a bulletproof vest. "So it raises the question, did he expect to escape from this and if so, what was all that intended for," Miller asked."