The investigation into the attempted assassination of Donald Trump at a rally in Butler, Pennsylvania continues. The House Oversight Committee will be briefed by Secret Service tomorrow regarding the shooting. There have been a lot of claims made on security at the event. Our National Investigative Unit is getting the facts on what is true and what isn't.We know the shooter was on a rooftop outside of the security perimeter. We still don't know, though, how he was able to get there without being stopped by law enforcement.There's been speculation about why the building Thomas Matthew Crooks climbed up was not covered by security. A source with the investigation told CNN that a local counter-sniper teams were supposed to be at the building and that it was noted as a designated post in the operational plan. The Pennsylvania State Police says they weren’t responsible for the area.Another accusation being made online is that Homeland Security denied requests made by Donald Trump's team to increase security. HHS Security Secretary Alejandro Mayorkas said that’s false. He even doubled-down saying they enhanced security back in June and no additional requests were made for more security.We have new information about a post making the rounds on social media. The poster claims to be from the sniper in the photo. It says his name is Jonathan Willis and that he had Crooks in his sights for at least three minutes, but Secret Service refused to give him the order to “to take out the perp.” Our partners at FactCheck.org say the Secret Service says this claim is “categorically false” and that they have no employee by that name.But here’s what we do know about the order of actions:Law enforcement sources told the AP they had reports of a suspicious person and went on a search for him. An officer climbed to the roof and encountered Crooks, who turned toward him. The officer couldn’t pull out his own weapon at that moment, so he retreated. That’s when Crooks fired shots at the former president.As the FBI continues to investigate, we will get a clearer picture of what happened at that rally and the days and weeks leading up to it.