Police stand near terrorists' vehicle in Texas
Police stand near terrorists' vehicle in TexasReuters

A Twitter account which appears to have belonged to one of the two gunmen shot dead outside a Mohammed Cartoon contest in Texas Sunday night, posted a message swearing allegiance to ISIS around the time of the attack.

The account, @atawaakul, has now been removed by Twitter. Its profile picture was a photo of Anwar al-Awlaki, the American-educated cleric who became the influential mouthpiece of Yemen's Al Qaeda in the Arabian Peninsula (AQAP) before being killed in a US drone strike.

In the message, the poster says: "The bro with me and myself have given ba'yah [allegiance - ed.] to Amirul Mu'mineen [leader of the believers - ed.], may allah accept us as mujahideen [holy warriors - ed.]"

Suspected gunman's tweet
Suspected gunman's tweetScreenshot

"Leader of the believers" is an Arabic reference to Islamic State (ISIS) leader and self-declared "caliph" Abu Bakr al-Baghdadi, who declared himself leader of the Muslim world when announcing his "caliphate" last year.

The tweet then ends with the worlds "Make dua" - possibly meaning "dawah," or spreading the word of Islam - and the chilling hashtag #texasattack.

There has been no independent confirmation that the account did indeed belong to one of the two shooters, but counterterrorism experts have speculated that the timing and the message are far too coincidental.

Previous tweets from the same account - whose username was Shariah is Light - included numerous posts glorifying ISIS and other jihadists.

Immediately after the attack, city of Garland said in a statement posted on its Facebook page that the two men drove up to the Curtis Culwell Center and began shooting at a security officer.

The statement added that Garland Police Department officers engaged the gunmen, who were both shot and killed.

The statement did not indicate, however, whether the shooting was related to the event, saying only the gunmen's vehicle may contain an "incendiary device." A bomb squad was dispatched to defuse it, and nearby businesses were evacuated.

If the Twitter account above is confirmed to have belonged to one of the gunmen, it would confirm suspicions that the attack was carried out by Islamists.

The American Freedom Defense Initiative was hosting a contest that would award $10,000 for the best cartoon depicting the Prophet Mohammed.