A lot of people think the assassination attempt is a conspiracy. No one knows for sure but the tidbits of information available make for great speculation.
If true; the Secret Service knew about the gunman a couple or few minutes before the 1st shot was fired. A spokeswoman for the SS said they did not go up on the roof because it was sloped and a safety hazard. That's got to be the most lame excuse I've ever heard. My personal speculation is the K9 ate their security plan.
It's one big puzzle.