By Richard A. Serrano and Matt Pearce, Los Angeles Times (TNS)

A federal law enforcement official confirmed Monday morning that one of two gunmen killed when they opened fire outside a controversial Muhammad cartoon event in Garland, Texas, is a known terrorist “wannabe” whom U.S. authorities had been tracking for some years.

Elton Simpson was prosecuted in 2010 in federal court in Phoenix for making false statements to FBI agents about going to Somalia to engage in jihad. He was found guilty of making the false statements, but the judge ruled that there was insufficient evidence to conclude that the crime was directly involved to “international terrorism.” Simpson was placed on 3 years’ probation and fined $600.

The source in Arizona said Simpson was from North Phoenix. The identity of the second gunman is unclear, the source said.

The two men were killed and a security guard wounded in an attack Sunday night outside the Muhammad Art Exhibit and Cartoon Contest, led by prominent conservatives who are critical of Islam.

The event was ending when two men drove up in a car and began shooting at a Garland school security officer, Bruce Joiner, who was apparently helping protect the building, city officials said.

“He was shot in the leg, transported to the hospital and he’ll be fine,” Garland Mayor Douglas Athas said.

The attack lasted just seconds, police said. One of the gunmen was shot immediately by police, and the other was shot and killed when he reached for a backpack, leading police to fear the men may have brought explosives, Athas said.

Officials evacuated the area as attendees were led away from the front of the building. Police searched for possible explosives late into the night.

The shooting in Garland, a suburb about 20 miles from Dallas, was preceded by messages from two social media accounts that expressed radical Islamic viewpoints.

One tweet, sent at 6:35 p.m., used the hashtag #texasattack. The user wrote, “May Allah accept us as mujahideen.” Attendees at the contest didn’t get word about the shooting until about 6:50 p.m.

Garland police spokesman Joe Harn said the department had not been aware of any credible threats against the event.

The gathering was organized by the American Freedom Defense Initiative, which is led by Pamela Geller, a well-known conservative political personality who has been harshly critical of Islam.

Classified by the Southern Poverty Law Center as an anti-Muslim hate group, the AFDI was behind controversial ad campaigns last year. Its ads on buses in San Francisco cast the Israeli-Palestinian conflict as a “war between the civilized man and the savage.”

Geller is perhaps best known for her opposition to what critics called the “ground zero mosque,” a cultural and prayer center that was to be built in New York about two blocks from the World Trade Center site.

In 2010, she led thousands of people in a march protesting the project, which has since been scrapped.

After the shooting, Geller posted an outraged statement on her blog. “This is a war,” she wrote. “This is war on free speech. What are we going to do? Are we going to surrender to these monsters?”

A cartoon on the AFDI’s website promoting the contest features a wild-eyed man in a turban wielding a sword, apparently the prophet Muhammad, and saying, “You can’t draw me!” The hand of an unseen artist replies, “That’s why I draw you.”

The Garland cartoon event was intended as a defiant gesture supporting free speech after the Jan. 7 terrorist attack on the Paris offices of the satirical magazine Charlie Hebdo. Two gunmen opened fire, killing 12 members of the staff and wounding 11 others.

The Charlie Hebdo attack was prompted by the magazine’s caricature of Muhammad. In Islam, depicting the prophet is considered a sacrilege.

French police identified two brothers with al-Qaida connections, Cherif and Said Kouachi, as the shooters. Both were later killed in a shootout with commandos.

The Garland contest reportedly received about 350 drawings of Muhammad and offered a top prize of $10,000, according to AFDI’s website.

It also advertised a $2,500 prize for the most popular cartoon, as voted by readers of Breitbart.com, a conservative website.

The keynote speaker was Geert Wilders, a right-wing member of the Dutch parliament. After seeking to ban the Koran, comparing the text to “Mein Kampf,” and calling Islam a totalitarian ideology, the controversial lawmaker faced charges of inciting hatred in the Netherlands, but he was acquitted in 2011.

Athas, Garland’s mayor, said the city was not associated with the politics of the event. “It really doesn’t have anything to do with Garland or Texas,” he said. “It just happened to be in our city. We provided security to make sure everybody would be safe.”

About 200 people attended, said Randy Potts, a contributing editor for the Daily Beast who was covering the event.

The center where the contest took place had been heavily guarded before the shooting, Potts said. “The security, as you can imagine, is pretty extensive,” he said. “Even before we came … maybe 50 to 100 feet away from the building, all around, was all blocked off.”

He was about to leave the center when “guys rushed up to us yelling, ‘Get back to the conference room!'” he said.

A livestream of the event captured a police official in tactical gear telling the calm crowd that two suspects and a policeman had been shot.

“Were the suspects Muslim?” an audience member asked.

“I have no idea right now,” the police official said, and attendees were ushered back into an auditorium as police attended to the scene outside.

Potts said he didn’t hear any gunfire, but that others inside had heard one to three gunshots.

“It’s pretty calm in here; people are telling jokes,” Potts said from inside the auditorium where the audience was taken. “We all know that security was so extensive we were not actually worried someone would actually get inside the building.”

Two social media accounts tweeted messages about the attack apparently before it happened.

A Twitter account titled “Shariah is Light” — bearing the image of extremist Islamic propagandist Anwar Awlaki, who was killed in an American drone strike in Yemen in 2011 — posted an allusion to the attack just minutes before it happened.

Before the shooting, the “Shariah is Light” account also tweeted a command to follow another account, titled “AbuHussainAlBritani,” which also tweeted before and after the attack.

“The knives have been sharpened, soon we will come to your streets with death and slaughter!” tweeted the “AbuHussainAlBritani” account before the attack.

After the attack, the “AbuHussainAlBritani” account began tweeting praise of the Texas shooting, and linked the attack to the militant group Islamic State.

“Allahu Akbar!!!!! 2 of our brothers just opened fire at the … art exhibition in texas!” the account tweeted. “Kill Those That Insult The Prophet.”

“They Thought They Was Safe In Texas From The Soldiers of The Islamic State,” the account tweeted.

The accounts have since been suspended.

Texas Gov. Greg Abbott condemned what he called the senseless attack in Garland and praised the police response. “This is a crime that was quickly ended thanks to the swift action by Garland law enforcement,” he said in a statement.

The FBI is providing investigative and bomb technician assistance, a spokeswoman said.

Late into the night, the two bodies were left on the street because of concerns that they might have explosives on them.

(Times staff writers Lauren Raab in Los Angeles and David Zucchino in Durham, N.C., contributed to this report. Serrano reported from Washington.), (c)2015 Los Angeles Times, Distributed by Tribune Content Agency, LLC.

Photo: (afp.com / Jared L. Christopher) Police officers gather May 4, 2015 in Garland, Texas