Karlsruhe, Germany ? U.S. Senior Airman Nicholas J. Alden was standing outside of a bus at Frankfurt Airport when a young man first asked him for a cigarette, then whether he was bound for Afghanistan.

When Alden answered yes, the 21-year-old Kosovo Albanian fatally shot him, point blank, in the back of the head, then stormed aboard the bus shouting “Allah Akbar” — Arabic for “God is great.” He shot and killed Airman 1st Class Zachary R. Cuddeback, who was at the wheel, then shot and injured two others, German authorities said Friday.

Gunman Arid Uka then pointed his FN 9mm pistol at yet another airman seated on the bus. “He pointed his pistol at his head and pulled the trigger twice, but the pistol jammed and no shots came out,” prosecutor Rainer Griesbaum told reporters in Karlsruhe.

Jammed, empty shell casing prevented the weapon from firing. Those casings saved up to six other lives — the number of cartridges left in the magazine.

Uka, who was raised and schooled in Germany, refused to speak Thursday when brought before a judge and formally charged with two counts of murder and three counts of attempted murder.

But shortly after the attack, he told police that he had taken the weapon and two knives to the airport specifically to kill Americans “as revenge for the American mission in Afghanistan,” Griesbaum said.

Uka said a YouTube video he saw the day before the incident allegedly showing a brutal raid on a home by U.S. soldiers in Afghanistan had inspired him to prevent what he considered “further atrocities.”

When he saw the busload of 16 airmen parked outside Terminal 2 awaiting transport to the nearby Ramstein Air Base, he approached Alden, 25, from South Carolina, who was assigned to the 48th Security Forces Squadron at RAF Lakenheath in England.

Cuddeback, 21, hailed from Virginia and was assigned to the 86th Vehicle Readiness Squadron at Ramstein Air Base in Germany. He was the only airman in uniform. The others were dressed in civilian cloths.

After his weapon jammed, Uka fled. The 22-year-old airman he last tried to shoot chased him into the airport terminal, where he and police overpowered the attacker.

The two U.S. airmen who were wounded have not been identified, and one of them remained hospitalized in critical condition on Friday.