WATCH: Video captures chaos of Trump rally assassination attempt | LiveNOW from FOX

The man who opened fire on a Trump campaign rally in Butler, Pennsylvania over the weekend apparently teased an attack online, days before shooting the former president.

FOX News reports that Secret Service and FBI officials told US Senators during an all-members briefing on Wednesday that Thomas Matthew Crooks wrote a threatening message on the faming platform, Steam, days before the attempted assassination.

Crooks allegedly wrote, “July 13 will be my premiere watch as it unfolds.” July 13 was the day that federal investigators said the 20-year-old climbed onto a rooftop and fired an AR-style rifle, killing a Trump supporter and wounding three people, including the former president.

Steam is a popular platform where tens of millions of gamers can purchase games and chat with other gamers. Investigators reportedly made the discovery during a review of Crooks’ devices, including his cell phone and laptop.

Benjamin Shrader was in attendance at the rally and captured video, where people can be heard screaming in the background after the gunshots were fired. You can hear people yell that someone has been shot.

Shrader joined LiveNOW from FOX’s Josh Breslow to share his experience and perspective.

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