evidence: Suspected Donald Trump rally shooter Thomas Matthew Crooks posted a cryptic message to to the online gaming website Steam that read "July 13 will be my premiere, watch as it unfolds" before he opened fired at the former president and his supporters on that date at a campaign stop in Butler, Pennsylvania, multiple outlets reported. [...] Crooks used an AR-style rifle, believed to be legally owned by his father, to shoot at Trump from the roof of a nearby building outside of his Butler, Pennsylvania, campaign rally last Saturday. [...] Details continue to emerge about Crooks and the circumstances of the rally shooting since Saturday, including that the building Crooks perched upon to shoot eight bullets at the former president was being used as a police tactical team staging area and was not swept by the Secret Service ahead of the event. How he was able to climb a ladder onto the roof without the notice of law enforcement officials who were stationed inside the building is still unclear and has become a sticking point as criticism of the Secret Service continues to mount. Crooks was found by a law enforcement officer on the roof of the building moments before shooting at Trump and pointed his rifle at the officer, the Associated Press reported, citing an anonymous source, who retreated from the roof moments before Crooks fired on Trump and was then shot by the Secret Service. The FBI has said its investigation so far suggests the shooter acted alone, however, "the FBI continues to conduct logical investigative activity to determine if there were any co-conspirators associated with this attack."