Source: Air Force shooter shouted "Allahu akbar"

The man accused of killing two U.S. airmen in Germany shouted "Allahu akbar" as he emptied his handgun aboard an Air Force bus, a U.S. law enforcement source told CBS News Thursday.

The source, who spoke on condition of anonymity, was reading from an official report about Wednesday's deadly shooting at Frankfurt airport. Arid Uka, a 20-year-old devout Muslim who officials say recently became radicalized, is being held in the deaths of the airmen and for seriously injuring two others, all of whom have not yet been publicly identified.

"They are at war with us," Uka told German police, according to the source.

German prosecutors released a statement saying "there is a suspicion that the act was motivated by Islamism," but it's not clear whether Uka was part of a terror group. German authorities have said that he was apparently not, but U.S. officials didn't rule out the possibility, according to the Associated Press.

The AP reported Thursday that Uka wasn't on any U.S. terror watch lists.

Uka had been loitering around the Air Force bus bearing U.S. military license plates before the shooting, CBS News' source said. The bus was transporting 15 airmen, who were traveling through Germany to Afghanistan from England.

The first deceased victim, who was wearing civilian clothes, was shot while boarding the bus, the source said. Uka then boarded the bus and shot the second deceased victim, the bus driver who was wearing a military uniform, the source said.

As Uka emptied his gun into the bus, he shouted "Allahu akbar," the Arabic phrase for "God is great," the source said. He then ran into the terminal, where he was captured by German police, the source said.