German authorities say a 21-year-old man from Kosovo is in custody, in the shooting attack on a bus carrying U.S. airmen outside the airport in Frankfurt.
Frankfurt police say the bus was sitting outside a terminal when the attack took place, leaving the driver and a passenger dead and another person with serious injuries. They say the attacker briefly entered the bus, and was caught when he tried to escape.
The Air Force says all four victims were airmen stationed at the Lakenheath base in Britain. It's home to the only F-15 fighter wing in Europe.
A German news agency quotes a security official as saying there are no indications of a terrorist attack.
But a member of the U.S. House Homeland Security Committee, Patrick Meehan, says that's what it looks like.
President Barack Obama is promising to "spare no effort" in investigating the slayings.
Lakenheath is home to the 48th Fighter Wing, the United States' only F-15 fighter wing. Its website says the base employs some 4,500 active-duty military members, as well as 2,000 British and U.S. civilians.
The motive for the attack was not immediately clear.