The man who killed five people in shootings this summer in Chattanooga, Tennessee, was inspired by foreign terrorist propaganda, FBI Director James Comey said Wednesday.

Comey made the comments while speaking at a news conference in New York.

“We have concluded that the Chattanooga killer was inspired by a foreign terrorist organization’s propaganda,” Comey told reporters, though he added the source of the propaganda couldn’t be determined and stopped short of mentioning a specific group.

“There’s competing foreign terrorist poison out there,” Comey said at the news conference. “But, to my mind, there’s no doubt that the Chattanooga killer was inspired and motivated by foreign terrorist organization propaganda. We’ve investigated it from the beginning as a terrorist case.”

Mohammad Youssef Abdulazeez opened fire at two military locations on July 16.

The Kuwait native and naturalized U.S. citizen first fired upon a recruiting center, then drove seven miles to a Naval reserve facility and opened fire again. The 24-year-old killed four Marines and a sailor, all of them located at the reserve, before he was killed in a shootout with police.

In a televised address to the nation from the Oval Office on Dec. 6, President Barack Obama called the Chattanooga shooting an act of terrorism. But authorities had offered little public detail about why they believed it was terrorism-related until Comey’s comments Wednesday.

Terrorist groups often use social media to spread propaganda and communicate, and federal lawmakers have proposed new bills to combat that in the wake of the Dec. 2 mass shooting that killed 14 people in San Bernardino, California. Obama has also called that an act of terrorism.