When Elton Simpson and Nadir Soofi opened fire at a perimeter security checkpoint at the event in May 2015, it was the first terror attack on U.S. soil for which the group ISIS claimed responsibility.

The security guard injured in the attack, Bruce Joiner, is suing the FBI in order to learn the extent of what the bureau knew in advance about the attack. In a related case, it was learned that an agent had been undercover in the ISIS cell for several months, and shortly after the "First Annual Muhammad Art Exhibit and Contest" was announced, the agent texted to Simpson, "Tear Up Texas."

Simpson and Soofi were both living in Phoenix at the time.

When the pair opened fire at the security checkpoint that day, the undercover agent was in a separate car directly behind the two men, and had been taking pictures just moments before the first shots were fired. The undercover agent then tried to flee, was apprehended by local police, and only then disclosed to them that he was an undercover FBI agent.

The two attackers were killed within yards of where they opened fire, but not before they hit Joiner in the leg. Joiner filed suit against the bureau last October.

Meanwhile, the same undercover agent is likely to take the witness stand in an Ohio courtroom sometime this month, possibly as early as this week, and will be allowed by the judge to disguise his appearance and use a pseudonym while testifying. The judge has further ruled that only the jury and essential court staff will be allowed in the courtroom during testimony.

Those wishing to observe the proceedings will be allowed to listen to an audio feed in a nearby overflow room, according to the Cleveland Plain Dealer.

In that case, federal prosecutors are charging Erick Jamal Hendricks with conspiracy to provide material support to a designated terrorist organization.

Hendricks is believed to have been one of the masterminds—if not the mastermind—behind Simpson and Soofi's attack in Garland.

Previously, the FBI told CBS's "60 Minutes" that, "There was no advance knowledge of a plot to attack the cartoon drawing contest in Garland, Texas."

However, a portion of the government's formal complaint against Hendricks shows that Hendricks told an FBI informant that future attacks by his "sleeper cell" would include attacks on, "the woman who organized the ‘Draw Prophet Muhammad contest,'" a reference to event organizer Pamela Geller.

Government attorneys in both cases have only ever asserted the undercover agent was in contact with Hendricks, and not with either Simpson or Soofi on the day of the attack.

In the case where Joiner is suing the government for the injuries he sustained in the attack, defense lawyers have argued, "[Joiner] can point to no further communications or interactions with Simpson before or during the event. Instead, Plaintiff tries to muddy the waters by referring to communications between UCE-1 and Hendricks."

Government Lawyers: 'Tear Up Texas' Text to Radicalized Islamist ...