U.S. authorities are trying to determine if there are any connections between the Islamic State group and two gunmen who attacked a contest in Texas where cartoonists drew pictures of the Islamic Prophet Muhammad.
Investigators have been looking at Twitter accounts linked to one of the men as well as electronic devices used by both.
Federal authorities confirmed Wednesday a Twitter account belonging to Elton Simpson, one of the gunmen killed Sunday at the event, posted a final tweet about 20 minutes before the shooting that said: "May Allah accept us as mujahideen," or holy warriors.
Among the hashtags used by the Twitter account was "#texasattack."
Was known to authorities
Texas Representative Michael McCaul, chairman of the House Homeland Security Committee who was briefed on the investigation, said the Twitter account linked to Simpson, 31, also included images of Anwar al-Awlaki, an American-born radical cleric killed in a CIA drone strike in Yemen.
But McCaul stopped short of saying law enforcement had missed a red flag.
"Was he [Simpson] on the radar? Sure he was," McCaul told The Associated Press from Turkey, where he was leading a congressional delegation. "The FBI has got a pretty good program to monitor public social media."
The Department of Homeland Security and the FBI issued a joint intelligence bulletin to Texas law enforcement April 20, warning the Garland event was a possible target for a terrorist attack, according to a DHS official who spoke to the AP but was not authorized to be quoted discussing the document.
Social media accounts linked to "violent extremists" had been focusing on the controversial cartoon contest, the bulletin said. Muslims consider any depiction of the prophet blasphemous.
Shortly after the shooting, police in Garland told Reuters that a bomb squad, the Federal Bureau of Investigation, a SWAT team and the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives had been involved in preparations for security around the exhibit, for which organizers reportedly paid $10,000.
It's unclear why Simpson and his roommate, Nadir Soofi, 34, were not stopped. The pair, wearing body armor, wounded a security guard in the leg before a Garland police officer shot and killed them at the scene.
On Tuesday, the Islamic State group claimed responsibility for the attack, saying "two of the soldiers of the caliphate" carried out the shooting in Garland, about 50 kilometers (30 miles) northeast of Dallas. It said this was its first attack on U.S. soil and that the worst is yet to come.
However, counterterrorism experts said the Islamic State group has a history of asserting involvement in attacks in which it had no operational role.
Congressman McCaul said the evidence does not indicate the attack was directed by the Islamist militant group, "but rather inspired by them."
White House spokesman Josh Earnest also said the Obama administration is not ready to pronounce that the Islamic State group has arrived in the U.S.
"There are extremists around the globe, including some who are affiliated with ISIL, who are trying to capitalize on the opportunity that's presented by social media to try to communicate with individuals around the world, including inside the United States," Earnest said, using an acronym often applied to the Islamic State group.
The families of both men say they were shocked by what happened and never saw any signs that either of them was capable of such violence.
Contacted after the shooting, Dunston Simpson, Elton Simpson's father, said his son "made a bad choice."
Shirley Dromgoole, Soofi's maternal grandmother, said, "It's just not like him, he wasn't that kind of person, I couldn't believe it when I saw on the TV, him getting out of the car with that AK-47 or whatever. I said, 'that can't be him,' but it was."
It's unclear at what point in his life Simpson turned radical, or how and when he met Soofi.
Simpson had worshipped at the Islamic Community Center of Phoenix for about a decade, but he quit showing up over the past two or three months, mosque President Usama Shami told AP.
Shami said Simpson would play basketball with mosque members and was involved in the community. Soofi, who owned a nearby pizza business, would stop in to pray occasionally, sometimes bringing with him his 8-year-old son, he added.
"They didn't show any signs of radicalization," Shami said.
Run-ins with the law
However, both men also had run-ins with the law, according to court records.
Court documents show that Simpson had also been under surveillance since 2006 and was convicted in 2010 of lying to FBI agents about his desire to join violent jihad in Somalia.
Utah court records show Soofi had several brushes with police during his time in the state. He pleaded to possession of alcohol by a minor, alcohol-related reckless driving and driving on a suspended license in 2001, court records show, and misdemeanor assault the following year.
The cartoon contest was sponsored by a group called the American Freedom Defense Initiative (AFDI), which offered a $10,000 prize for the best drawing of the prophet.
Robert Spencer, who runs the website Jihad Watch and is a co-founder of AFDI, said the attempt to disrupt the controversial contest is motivation for him to hold another one.
"We kind of have to do it again," Spencer told Reuters by telephone, adding that not doing so would amount to giving militants the power to censor.
Some material for this report came from AP and Reuters.