After police killed two gunman who tried to ambush a Garland, Texas event featuring controversial cartoons of the Muslim Prophet Mohammed, details began to emerge about the shooters.

One suspect, identified as Elton Simpson by a federal law enforcement source, linked himself to ISIS in a tweet posted just before the attack. He was no stranger to federal investigators. In 2011, he was convicted of making a false statement involving international and domestic terrorism.

The other suspect, identified as Nadir Soofi by two federal law enforcement officials, was Simpson’s roommate in a Phoenix apartment. He wasn’t well-known to federal law enforcement and was not on the FBI’s radar, one of the officials said. Officials stated that investigators are going through evidence retrieved from the shooters’ homes in Arizona to help piece together a timeline of how their plot came together.

Simpson and Soofi never made it inside the Curtis Culwell Center in Garland, where they were targeting cartoonists. In addition to the cartoon contest, a right-wing Dutch politician who’s on an al Qaeda hit list was speaking Sunday evening.

Garland Police Department spokesman, Joe Harn, told reporters Monday, a traffic officer working after-hours as security for the event and armed only with a service pistol killed both men. Both men were wearing body armor and carrying assault rifles.

“He did what he was trained to do, and under the fire that he was put under, he did a very good job. And probably saved lives,” Harn said of the unidentified officer. “We think their strategy was to get into the event center, and they were not able to get past our perimeter that we had set up.”

Only a few questions remain. Was this an attack from ISIS and are there links to ISIS? Simpson posted a tweet before the attack that read, in part, “May Allah accept us as mujahideen.” That tweet from Simpson also said he and his fellow attacker had pledged loyalty to “”Amirul Mu’mineen” (the leader of the faithful), which CNN terrorism analyst Paul Cruickshank said probably refers to ISIS leader Abu Bakr al Baghdadi.

After the shooting, an ISIS propagandist that Simpson had earlier asked his readers to follow tweeted, “Allahu Akbar!!!! 2 of our brothers just opened fire” at the Texas event.

In 2011, Simpson was convicted of making a false statement involving international and domestic terrorism and was sentenced to three years of probation, court records show. Prosecutors said he told FBI agents that he had not discussed traveling to Somalia to engage in a “violent jihad” when, in fact, he had, according to an indictment reviewed by CNN.

U.S. authorities are investigating whether Sunday’s shooting has any link to international terrorism. Other sources have acknowledged Simpson’s tweet could indicate the attack was inspired by ISIS, but not orchestrated by the group.