The FBI was well aware of one of the Texas terror shooting suspects

One of the two shooters killed during an attack on a Texas art show and contest featuring depictions of the Prophet Muhammad was reportedly the subject of a previous FBI terror investigation.

Elton Simpson and an accomplice stormed a Garland, Texas community center Sunday afternoon but were shot dead by security officers before being able to take any lives. Simpson was known to authorities at least five years ago, an FBI official told ABC News. 

Simpson was convicted in 2010 for lying to investigators about his intentions during a planned trip to Somalia, according to court documents reviewed by Business Insider.

"The defendant falsely stated to special agents of the FBI that he had not discussed traveling to Somalia, when in fact he had discussed with others traveling to Somalia for the purpose of engaging in violent jihad," the affidavit said.

An informant recorded multiple conversation with Simpson in which he discussed an urge to travel to Africa and join other jihadists because "fighting non-Muslims in other countries was the way to get to heaven," according to the filing.

Despite finding that Simpson lied about his Africa travel plans, Judge Mary H. Murguia ruled the feds did not provide sufficient proof he planned to join a terror group upon arrival.

A Twitter account attributed by authorities to Simpson tweeted multiple threatening messages just before the attack, including one with the hashtag #texasattack, according to WFAA. The account has since been suspended by Twitter. 

The assault came after ISIS supporters reportedly spent weeks online calling for an attack on the event, authorities said. 

A notorious ISIS terrorist reportedly tweeted shortly after the attack: "Kill those that insult the prophet #GarlandShooting." 

NBC5

Officials have not named Simpson's accomplice but told a Phoenix television station that their investigation led back to Arizona.

"The two gunmen who were involved in the shooting in Dallas... were determined to be from Phoenix, located at this property," Assistant Special Agent in Charge John Lannarelli told KPNX, according to Dallas television station WFAA. 

"Hence the FBI and Phoenix police were involved in determining where at this location and what evidence may be available that can be used in the Dallas investigation." 

One unarmed security guard, identified by WFAA as Bruce Joiner, was injured in the attack but is expected to make a full recovery.

Simpson and his accomplice are believed by investigators to have been roommates living in Phoenix, Arizona.

SWAT officers and FBI agents stormed the pair's apartment early Monday morning, according to KPNX. Phoenix police entered the apartment just after 3:00 a.m., according to the station.

Agents are searching the residence for further evidence.