A man shot in the leg during a 2015 terrorist attack is pushing the FBI to explain why one of its agents was at the scene and did nothing, and if the agent was filming the incident for the terrorists as part of his undercover work of trying to infiltrate the group.

Bruce Joiner was working security for the controversial "Draw Muhammad" event in Garland, Texas, when two radical Islamic extremists, Elton Simpson and Nadir Soofi, pulled up to the parking lot checkpoint where he was stationed. The two opened fire at the checkpoint.

Simpson and Soofi were wearing body armor and had arrived at the event in a car stocked with firearms and hundreds of rounds of ammunition. But because the "Draw Muhammad" event was so controversial, it was also well-guarded.

A traffic officer quickly shot the attackers just yards away from where they started shooting. Joiner was the only casualty in what became the first attack on American soil in which the Islamic State claimed responsibility.

But in the last few weeks, it became clear that in the car immediately behind Simpson and Soofi was an undercover FBI agent, who was also taking pictures of the scene just seconds before they opened fire. Once the shots were fired, the undercover FBI agent tried to flee the scene, according to a recent report by 60 Minutes.

Revelations through court proceedings have also shown that the agent was undercover and in contact with Simpson for several weeks leading up to the attack. At one point a few weeks before the attack, the agent had texted Simpson the message, "Tear up Texas."

Joiner wants answers, and because the FBI has recently refused to answer his questions, he's now free to sue the bureau. The question he's asking is: Is the FBI's undercover work so important that it's willing to allow a terrorist event to take place just to maintain the operation?

Joiner's attorney, Trenton Roberts of Houston, believes the FBI agent did decide to stand down in order to keep his cover. Roberts says because there are so many unusual facts to that day, only one or two theories can actually fit all the evidence.

"It seems like it had to have been one or the other," Roberts told the Washington Examiner. "Just a complete botched operation where they [the FBI] don't want the attack to actually take place, or, it's something where they need the attack to take place in order for this guy [the agent] to advance in the world of ISIS."

"And that's really what I think. I think that they thought, 'he's undercover and in order to advance, he needed to get pictures or video of this attack,' and then that would bolster his street cred within ISIS," Roberts said.

Roberts said he and his client didn't start off by pushing conspiracies as to what happened that day. He also said his client would prefer to really know what happened that day over taking a settlement check from the government to make his case against the FBI go away.

"It is accusatory," Roberts acknowledged of his theory. "But at this point, I do feel like when the FBI has given so few answers, and there's been so many opportunities to do so, you have to conclude that there must be something really worth covering up."

The FBI declined to comment for this story, a position it has taken with all other major media reports about the Garland attack.

"Bruce is very pro-law enforcement overall, he's a former police officer, and a current security guard, and so he just wants a full explanation," Roberts said. "At the beginning, he thought, 'Surely they have some kind of explanation that actually is going to make sense.'"

"But then as the facts began to come in, it was clear that [this agent] was in some way involved in the planning of it, and was there at the scene," he said. "And just that they won't give the victim an explanation, has surprised us all."

Sen. Ron Johnson, R-Wis., is also pressing for answers from the FBI. As the chair of the Homeland Security and Governmental Affairs Committee, Johnson recently sent a letter to FBI Director James Comey asking him to explain what appear to be conflicting statements about the FBI's activities leading up to the Garland attack.

However, the deadline for responding to Johnson's request has passed and the FBI did not turn over any information.

Joiner and his attorney have six months to decide if they will proceed and sue the FBI.

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