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FILE - This photo taken from video provided by WEAR-TV shows emergency responders following a shooting incident at Naval Air Station Pensacola, in Pensacola, Florida, Dec. 6, 2019.

Al-Qaida in the Arab Peninsula (AQAP) claimed responsibility Sunday for an attack on a U.S. Naval Base which left three soldiers dead in December, the Site intelligence group reported.

"Alshamrani carried out his martyrdom operation on one of the dens of evil...the US Naval Air Station Pensacola," the group's leader said in a video message posted Sunday, referring to Mohammed Alshamrani, a 21-year-old second lieutenant in the Royal Saudi Air Force training at Naval Air Station Pensacola who carried out the attack late last year.

AQAP leader Qassim al-Rimi said in the video that Alshamrani moved around U.S. bases "for several years" to assess a target.

Alshamrani killed three U.S. servicemen and injured eight others in a classroom on the base Dec. 6.  

At the time, investigators found no evidence that Alshamrani was affiliated with a terrorist group, but they learned that the cadet had posted anti-American and anti-Israel content on social media in the lead up to the shooting, including a message posted Sept. 11 that said "the countdown has begun."

Twenty-one Saudi military trainees were sent back to Saudi Arabia following a probe in the wake of the attack.