The suspects have been identified as Elton Simpson and Nadir Soofi.
A Garland police officer who was armed with only a handgun fatally shot the suspects, who were armed with assault rifles and body armor, outside of the Curtis Culwell Center.
"He did what he was trained to do. Under the fire he was under, he did a very good job and probably saved lives," said Garland Police Department spokesman Joe Harn. "We think the men intended to get inside the event and this officer kept them from getting inside and doing more harm."
Authorities are still investigating whether the attack was a terrorist attack, but "obviously they were there to shoot people," Harn said during a press conference Monday morning.
The shooting at the Curtis Culwell Center happened just as Sunday's night's "Draw the Prophet" event was coming to an end.
The suspects drove up, got out of their car and without saying anything, opened fire on an unarmed Garland Independent School District security officer. A Garland police officer returned fire with his duty pistol, killing both suspects, Harn said.
The Garland ISD security officer, identified as 8-year veteran Bruce Joiner, was hit in the leg during the shootout. He was treated at a local hospital and has since been released.
One witness talked to FOX 4 News about the chaos.
"We're almost to the parking lot, and we start hearing officers blowing their whistles, yelling," said Nathan Basetto. "We have no idea what all the commotion is and we start looking around. There's gun drawn and we have no idea what's going on. Finally, there's been reports of gun shots and two suspects have been shot dead."
Suspects' Car and Apartment Searched
The crime scene outside the Garland events center remained active Monday as FBI agents searched for evidence.
Before dawn, a bomb squad detonated several suspicious items inside the gunmen's car. Video from SKY 4 showed charred ground around the car and explosive damage, but Harn said there were no bombs found inside.
Harn mentioned investigators found luggage and extra ammunition inside the car.
The bodies of the gunmen were not immediately taken away because they were too close to the car. They were removed once the scene was clear.
Simpson and Soofi roomed together in an apartment that was searched by investigators Monday in Phoenix, Ariz.
Video from FOX 10 in Phoenix showed investigators working out of white vans outside the apartment complex.
Federal officials tracked Simpson on and off since 2006. He was arrested by FBI agents in 2010 under suspicions that he lied to authorities regarding a planned trip to Africa, and he received three years of probation.
About 20 minutes before the attack, there was a posting on a radical jihadist Twitter account indicating that two people were going to sacrifice themselves and that posting including #TexasAttack.
Investigators are still working to determine if those tweets are connected to the case, Harn said.
Event Center Evacuated
The Curtis Culwell Center, a public events space owned by the Garland Independent School District, was evacuated after the shooting.
About 200 people were taken from the building by bus to a separate location. They were held for a few hours and questioned by FBI agents, then released. Harn said many of them went back to hotels.
Several nearby businesses were also evacuated, including a Walmart store.
Store employees told FOX 4 they heard gunfire, but at first no one took it seriously because they just assumed someone had dropped something. They just continued working until they got the shocking news.
"We don't usually see Walmart empty like this. It's usually packed and everybody is wondering what's going on," a shopper said.
The evacuation was lifted several hours later, but a large area around the center remained cordoned off late into the night.
Garland school district officials said Monday classes on all campuses were being held as normal, but extra security was brought in for the day.
Advanced Placement testing scheduled at the center for Monday was moved to the local high schools, the district said.
Art Exhibit Controversy
Harn said it was not immediately clear that the shooting was connected to the contest hosted by the New York-based American Freedom Defense Initiative. During the event $10,000 was awarded for the best cartoon depicting the Prophet Muhammad.
According to mainstream Islamic tradition, any physical depiction of the Prophet Muhammad -- even a respectful one -- is considered blasphemous. Drawings similar to those featured at the Garland event have sparked violence around the world.
In January, 12 people were killed by gunmen in an attack against the Paris office of the satirical newspaper Charlie Hebdo, which had lampooned Islam and other religions and used depictions of Muhammad. Another deadly shooting occurred the following month at a free speech event in Copenhagen featuring an artist who had caricatured the prophet.
Tens of thousands of people rallied around the world to honor the victims and defend the freedom of expression following those shootings.
The Garland event featured speeches by American Freedom Defense Initiative president Pamela Geller and Geert Wilders, a Dutch lawmaker known for his outspoken criticism of Islam. Wilders received several standing ovations from the crowd and left immediately after his speech.
Wilders, who has advocated closing Dutch doors to migrants from the Islamic world for a decade, has lived under round-the-clock police protection since 2004.
Geller told the AP before Sunday's event that she planned the contest to make a stand for free speech in response to outcries and violence over drawings of Muhammad. She said in a statement issued after the shooting that it showed how "needed our event really was."
Harn said the school district normally hires security for events at its facilities and additional security was hired for Sunday's event.
The sponsoring group spent about $10,000 on off-duty police officers and other private security.
"An enormous amount of preparation for security went into this event, not just for the Garland police and as you can see there's a Bearcat or some vehicle outside. You have soldiers and our personal security team as well, tens of thousands of dollars that we have invested," Gellar told FOX 4 before the shooting.
Harn believes the level of security was sufficient. Teams from the FBI and ATF, as well as other local police departments, were also there assisting.
He said the city had not received any credible threats.
"We have people who conduct intel to keep our citizens safe every single day. There was no doubt they saved lives," he said.
Texas Gov. Greg Abbott released a statement about what he called a "senseless attack."
"Texas officials are actively investigating to determine the cause and scope of the senseless attack in Garland, Texas. This is a crime that was quickly ended thanks to the swift action by Garland law enforcement. Our thoughts and prayers remain with all those affected tonight," Abbott said.
Sen. John Cornyn said "an attack on free speech is an attack on all Americans." He was thankful that the officers involved prevented a bad situation from becoming much worse.
The Anti-Defamation League, an organization that fights anti-Semitism, condemned the attempted violence.
"No matter how offensive an event or program may be, there is no place in our community or our country for such violence," the ADL said.
Some who were at Sunday's event told FOX 4 that the art contest was all about free speech and that the shooting highlights the need for more awareness of terrorists in the U.S.
Reactions from Local Muslim Groups
Local Muslim groups publicly condemned the actions of the gunmen.
The Ahmadiyya Muslim Community in Allen says violence is never an acceptable response to what it calls anti-Islam events.
The group says it stayed away from the contest and art exhibit and asked fellow Muslims to do the same.
The president of the Dallas chapter says if the gunmen were acting in the name of Islam, they do not represent North Texans of the same faith.
The Associated Press contributed to this report.
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