The fatal shootings at a Navy reserve facility in Chattanooga, Tennessee, in July were "motivated by foreign terrorist organization propaganda," FBI Director James Comey told reporters on Wednesday, according to CNN.
Mohammod Youssuf Abdulazeez opened fire on a military recruiting center, then drove seven miles away to a Navy reserve facility, where he shot and killed four Marines and a sailor.
"There is no doubt that the Chattanooga killer was inspired, motivated by foreign terrorist organization propaganda," Comey said on Wednesday, though he added that it is difficult to determine which terrorist group may have inspired Abdulazeez.
FBI officials had previously said they don't have "anything that directly ties" Abdulazeez to any foreign terrorist organizations, although experts said his behavior fits the mold of attacks Islamic State (ISIS) has called for.
But Comey made clear on Wednesday that the FBI has been investigating the shootings as a terrorism case from the outset.
His comments mark the first time a U.S. official has provided details outlining why the Chattanooga shootings are thought to be an act of terrorism.
Earlier this month, President Barack Obama cited the Chattanooga shootings along with the recent San Bernardino, California, attacks as terrorist incidents but did not elaborate.
Counterterrorism investigators were looking closely at a 2014 trip to Jordan by Abdulazeez, trying to determine whether he had contact with any extremists or traveled to other countries from Jordan.
Some reports indicated that Abdulazeez was in Qatar at least once during his 2014 trip to the Middle East, but reasons for the stopover were unknown.