U.S. officials say the gunman in a deadly attack at a military base in Pensacola, Florida, last December was meticulous in his planning and had been radicalized overseas for at least five years.

The FBI says it has found a link between the gunman in the attack late last year at the Pensacola Naval Air Station and an al-Qaida operative.

The gunman was killed by a sheriff’s deputy during the rampage at a classroom building, where he had been undergoing flight training.

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