PHOENIX (AP) - About 20 minutes before the shooting at a Texas cartoon contest that featured images of the Prophet Muhammad, a final tweet posted on an account linked to one of the gunmen said: "May Allah accept us as mujahideen," or holy warriors.
Among the hashtags used by the account was "#texasattack."
Federal authorities confirm the Twitter account belonged to 31-year-old Elton Simpson, a Phoenix man who, along with another gunman, opened fire Sunday in the Dallas suburb of Garland, said Rep. Michael McCaul, chairman of the House Homeland Security Committee. The Texas congressman was briefed on the investigation by federal law enforcement officials.
McCaul said the Twitter account linked to Simpson included images of Anwar al-Awlaki, an American-born radical cleric killed in a CIA drone strike in Yemen. But the congressman stopped short of saying law enforcement had missed a red flag.
"Was he on the radar? Sure he was," McCaul said 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 local law enforcement on April 20 warning that the Garland event was a possible target for a terrorist attack, according to a DHS official who was not authorized to be quoted discussing the document.
Social media accounts linked to "violent extremists" had been focusing on the contest, the bulletin said. According to mainstream Islamic tradition, any physical depiction of the Prophet Muhammad - even a respectful one - is considered blasphemous.
And a federal law enforcement official said authorities had an open investigation into Simpson at the time of the shooting. The official was not authorized discussing ongoing investigation by name and spoke on condition of anonymity.
It's unclear why Simpson and his roommate, Nadir Soofi, were not stopped. A security guard was wounded in the leg before the gunmen were killed at the scene.
The law enforcement official said investigators will be studying the contacts the men had prior to the shooting, both with associates in the U.S. and abroad, to determine any additional terror-related ties.
The Islamic State group claimed responsibility Tuesday for the shooting, but counterterrorism experts said IS has a history of asserting involvement in attacks in which it had no operational role.
That suggests the two gunmen could have carried out their own lone wolf-style strike.
The evidence does not indicate the attack was directed by the Islamic State group, "but rather inspired by them," McCaul said. "This is the textbook case of what we're most concerned about."
The postings on the Twitter account linked to Simpson contrast sharply with the impression the jovial man and his quiet, 34-year-old roommate gave to neighbors and the leader of the mosque, which they attended in Phoenix up until recently.
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.
Both men had had run-ins with the law, according to court records.