4pm Update: Garland PD says they had info on the suspects' identities.

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GARLAND (CBSDFW.COM/AP) – CBS 11 News has confirmed the FBI issued a warning to the Garland Police Department approximately 3 hours before the attack on the Curtis Culwell Center Sunday.

Social media comments through outlets like Twitter sent up the red flag. “I know there are other Elton Simpsons out there,” FBI Director James Comey said Thursday.

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.”

Suspects Elton Simpson and Nadir Soofi were shot and killed after they opened fire. Garland Police Department Public Information Officer Joe Harn told CBS 11 on Sunday that their officers were “prepared” for the shooting at the Muhammad art event.

Garland police wouldn’t offer any specifics Thursday afternoon about any bulletin provided by the Feds, but dispute any talk of an early warning for violence that would come specifically from Simpson.

“So far as knowing these two guys were on their way to Garland from Garland, we did not know that,” said Harn on Thursday.  “Any names specifically, pictures, I refer you back to the FBI .  A vehicle pulled up. They got out and started shooting. That’s when we knew they were there.”

“We (FBI) didn’t have reason to believe that he (Simpson) was going to attack the event,” said FBI Director James Comey.  “Agents didn’t have reason to believe he had left Phoenix.  But because we developed reason to believe that he might be interested in the event, we sent the bulletin to them (Garland police).”

There was no actual threat information regarding Simpson.

According to the Associated Press, Simpson, of Phoenix, had been convicted in 2011 in a terrorism-related investigation and sentenced to probation. The FBI opened a new investigation into his activities in March. Comey said that investigation was “open but far from complete” at the time of the shooting.

The New York Police Department is investigating a threat against the exhibit’s organizer, Pamela Geller.

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