Investigators have not ruled out terrorism in a deadly shooting outside at a Texas arena that was hosting a “Draw Muhammad” contest.

"We’re certainly looking into that," Garland County Police Department spokesman Joe Harn said Monday at a news conference. "We have not knocked that out."

Security officers in Dallas shot and killed two alleged gunmen on Sunday night outside the Curtis Culwell Center in Dallas, where a conservative group held an art exhibit that featured a contest for best cartoon of the Muslim Prophet Mohammad. Some Muslims find such depictions of the prophet to be offensive.

Harn said the two assailants pulled up to an entrance of the building where two officers were stationed carrying assault rifles. The men then opened fire, Harn said.

One officer was shot in the leg, while the other shot and killed both of the assailants. A SWAT team on the site quickly responded to the shooting, Harn said.

The organizers of the event had paid $10,000 for extra security, including off-duty Garland Police Department officers.

Harn also said officers did not find explosives in the car that belonged to the gunmen.

Police are investigating motives for the attack and are combing through the backgrounds of both men, according to multiple reports.

While Harn declined to release the name of the suspects, law enforcement officials told the New York Times that one of them was Elton Simpson of Phoenix. Authorities are said to be searching his apartment there.

The event in Dallas was organized by the American Freedom Defense Initiative, which the Southern Poverty Law Center has labeled an extremist anti-Muslim group. The group rejects that criticism as coming from the “radical left” and says it is standing up for freedom of speech.

Harn said that in the time leading up to the event, there had been “chatter” about a possible threat without anything specific.

He praised the off-duty police officer, usually assigned to traffic duty, who shot the men.

“He did what he was trained to do and under the fire that he was put under he did a very good job,” Harn said. “And probably saved lives.”

— This story was updated at 12:22 p.m.