I agree with your main point, but the shooter apparently didn't go completely unnoticed before the shooting:
>>>Law enforcement sources also told CBS that he was reported by a bystander and identified as a suspicious person by police, but that officers lost track of him before the shooting began.<<<
The 20-year-old registered Republican purchased ammunition the day of the rally, authorities say.
www.bbc.com
>>>Rallygoers alerted local police of a suspicious person near the magnetometer area, two senior officials said. They tried to search for the suspicious person, believed to be Crooks, but could not find him in the crowd, the officials said.
Two municipal officers also tried to approach Crooks shortly before he opened fire, according to two senior officials. It is unclear where that took place.<<<
Trump said in a post on Truth Social that he “was shot with a bullet that pierced the upper part of my right ear.”
www.nbcnews.com