Authorities are investigating whether the Islamic State may have been linked to Sunday evening's attacks on a Texas free speech event after a trail of social media messages from before the event were discovered.
A Twitter account called "Shariah is Light" posted a message with the hashtag "texasattack." The account featured a picture of Anwar Awlaki, an American-born cleric killed in 2011 by a drone strike in Yemen,
the Los Angeles Times reported.
The Twitter account also posted a message asking people to follow a second account called "AbuHussaidAlBritani." That account posted several messages mentioning the Texas shooting and appeared to link it to the Islamic State.
That evening, two men drove to the Curtis Culwell Center in Garland, Texas, and opened fire on an outside exhibit of caricatures of the Prophet Muhammad. The suspects were gunned down after shooting a security guard in the leg.
The event had been organized by an anti-Islamic group and publicized as a free speech event. It offered a $10,000 prize for the best caricature of Muhammad. Followers of Islam consider any physical depictions of the prophet as blasphemous.
The first message on the Twitter account read: "The knives have been sharpened, soon we will come to your streets with death and slaughter!" A second message said: "Allahu Akbar!!!!! 2 of our brothers just opened fire at the Prophet Muhammad art exhibition in texas!"
"Kill Those That Insult The Prophet," a third message said.
A final message from the account said: "They Thought They Was Safe In Texas From The Soldiers of The Islamic State."
The FBI has named one of the gunmen as Elton Simpson, a former terrorist suspect,
ABC News reported. Agents and a bomb squad were sent to his apartment in Phoenix and used a robot to sweep his home.
He was previously convicted of lying to federal agents about traveling to Africa five years ago but a judge ruled that there was no proof that he was going to join a terrorist group, and he was ultimately placed on probation.
According to the Daily Mail, authorities believe Simpson may have been behind the Twitter messages with the final message being shared about 30 minutes before the attack.
For more than a week, Islamic State (ISIS) followers had been calling for an attack after hearing about the "draw Muhammad" art contest.
After the attack, the SITE Intelligence Group reported that an Islamic State fighter said on Twitter that the shooting was carried out by two pro-Islamic State supporters, the Mail reported. And other Islamic State supporters claimed on Twitter that one of the gunmen was the man calling himself "Shariah Is Light."
Earlier this week he had posted a message that said, "the bro with me and myself have given bay'ah [oath] to Amirul Mu'mineen [ISIS leader Abu Bakr al-Baghdadi]. May Allah accept us as mujahideen #texasattack."
The shooting was reminiscent of past attacks or threats in other Western countries against
art depicting the Prophet Muhammad. In January, gunmen killed 12 people in the Paris offices of French satirical magazine Charlie Hebdo in revenge for its cartoons.
In February, a masked gunman opened fire on a Copenhagen meeting attended by a Swedish artist who had been threatened with death for his cartoons of the Prophet Muhammad. A civilian was killed and three police officers were injured in the attack, aimed at artist Lars Vilks. His drawings, which depicted the Prophet Muhammad as a dog, stirred controversy in 2007.