Agent is at the center of ongoing questions over FBI's activities in run up to the attack

The undercover FBI agent who was just yards away from a terrorist attack in Garland, Texas, in 2015 testified in court on Wednesday that he was surprised to see the attack happening.

The agent's testimony came in the federal government's prosecution of Erick Jamal Hendricks, who is accused of recruiting and organizing two other radicalized Islamists to carry out the attack on the "First Annual Muhammad Art Exhibit and Contest" in May of that year. The attack was the first ISIS-backed terror event on U.S. soil.

The undercover agent's role in the attack has been the source of controversy because court filings show he told one of the eventual attackers to "Tear up Texas" in a text message just days after the "Draw Muhammad" event was announced.

The two attackers, Elton Simpson and Nadir Soofi, were residents of Phoenix but drove to Garland for the event, opening fire at a checkpoint on the perimeter of the parking area. Because of the controversy surrounding the event, security was high, and, as a result, Simpson and Soofi were killed within yards of where they began their assault. The ensuing investigation found the pair had several other guns in the vehicle and hundreds of rounds of ammunition.

Besides the "Tear up Texas" message, the undercover agent was also discovered to have been in a separate vehicle that was directly behind Simpson and Soofi's car when the shooting began. After the first shots were fired, the agent tried to flee the scene, but was quickly apprehended by local police.