'Draw Muhammad' shooting in Texas: 5 things to know

Texas police shot dead two gunmen armed with assault rifles who opened fire outside of a "Draw Muhammad" contest organized in the town of Garland on Sunday.

Federal law enforcement sources on Monday confirmed that one of the suspects in the shooting is Elton Simpson. The second suspect is Nadir Soofi, who is Simpson's roommate, senior law enforcement officials told NBC News. Their apartment was being searched in North Phoenix. At this point, it is unclear whether the suspects were linked to international terror groups, but federal agents are investigating.

Simpson was known to the FBI and was convicted of lying to federal agents five years ago about his plans to allegedly join a terror group in Africa.

"While all the facts are not in yet, last night's attack serves as a reminder that free and protected speech, no matter how offensive to some, never justifies violence of any sort," Homeland Security Secretary Jeh Johnson said in a statement Monday evening, adding that "we urge that members of the public not misdirect anger and suspicion at those simply because of their religious faith."

Here's a look at what we know about the incident — from the event to the attackers.

RELATED: Two suspects killed, guard shot outside ‘Draw Muhammad’ contest in Texas

Who organized the event?

The inaugural Muhammad Art Exhibit and Contest offered a $10,000 prize for cartoons of the Islamic prophet — depictions that are considered blasphemous by many Muslims around the world.

The event was sponsored by the American Freedom Defense Initiative (AFDI) and attended by its president and co-founder, Pamela Geller — who is also president of Stop Islamization of America (SIOA). Both are listed as hate groups by the Southern Poverty Law Center (SPLC).

Geller, a prominent campaigner against plans for a mosque near Ground Zero, is author of "The Post-American Presidency: The Obama Administration's War on America." In 2013 she was reportedly barred from entering Britain, where she was due to speak at a rally organized by the far-right group English Defense League.

"This is a war. This is war on free speech," Geller wrote on her website Sunday. "What are we going to do? Are we going to surrender to these monsters? Two men with rifles and backpacks attacked police outside our event. A cop was shot; his injuries are not life-threatening, thank Gd [sic]. Please keep him in your prayers. The bomb squad has been called to the event site to investigate a backpack left at the event site. The war is here."

Geller penned several others posts about the shooting, including claiming the British newspaper The Daily Mail blacked out cartoons of Muhammad from the event. "The cowardice of the enemedia has reached monstrous proportions. They will stop at nothing to appease bloodthirsty jihad terrorists. They are not journalists. They are water-carriers for the forces of oppression, hatred, and forcible censorship," she wrote.

The SPLC describes Geller as the "anti-Muslim movement's most visible and flamboyant figurehead," adding, "she makes no pretense of being learned in Islamic studies." 

Geller's group, the American Freedom Defense Initiative, also gained infamy in 2012 for an advertisement in the New York City subway system that criticized Islam. “In any war between the civilized man and the savage, support the civilized man. Support Israel. Defeat Jihad," the ad said.

Among the speakers present was outspoken anti-Muslim Dutch politician Geert Wilders, who later tweeted a picture of himself in front of what he called a "SWAT team" of armed police officers.

What happened?

Officials said about 200 people attended the heavily policed event at the Curtis Culwell Center in the Dallas suburb of Garland. As the event was drawing to a close, two gunmen armed with assault rifles drove up to the venue and began shooting, wounding school district security guard Bruce Joiner in his lower leg. Garland police officers returned fire, killing the men.

The name of the officer who took down the gunmen was not immediately released. "He did what he was trained to do," Garland police spokesman Joe Harn told reporters Monday. "Under the fire that he was put under, he did a very good job. And probably saved lives."

A video live stream from inside the event showed participants being told by armed police to move into a secure room away from the front of the building. Shoppers at a nearby Walmart were ordered away from the scene by police.

Harn said that a SWAT team responded to the scene within seconds. The gunmen were killed next to their car, Harn said, noting that there were multiple shots fired at the scene. "There's a lot of casings out there," he said.

When asked whether the shooting was considered a terror attack, Harn said "we’re certainly looking into that. We have not knocked that out."

Harn added that he did not expect any other immediate arrests in the case.

Why was it held at a school arena?

The Curtis Culwell Center was chosen because it had previously hosted an Islamic conference — Stand With the Prophet in Honor and Respect — in January. That event was held one week after gunmen in France attacked and killed 12 people at the Paris offices of Charlie Hebdo, a satirical magazine that had published cartoons depicting Muhammad. The AFDI picketed the January conference and moved to hold its own event.

Some had questioned whether the Garland Independent School District, which runs the venue, should allow the event to go ahead.

However, school board President Rick Lambert told the Dallas Morning News that the convention center was a public facility and the district could not discriminate based on viewpoints. The AFDI paid approximately $10,000 for additional security at Sunday's cartoon contest, the newspaper reported.