A police spokesperson said it was too early to determine if the attack was politically motivated or a planned act of terrorism. It has been reported that the shooter, identified as a Muslim in his early 20s, shouted "Allah Akbar" ("God is greatest") before opening fire.
The gunman apparently approached the bus full of airmen around 3 p.m. local time and shot and killed a soldier standing in front of the vehicle before killing the bus driver and wounding two other passengers, said Boris Rhein, Interior minister for the state of Hesse.
"I am consciously speaking of homicide and not an attack," Mr. Rhein said at the scene. "But at the moment, nothing can be ruled out."
The airmen are based in the UK at the Lakenheath Airfield in Eastern England, which is home to the only F-15 fighter wing in Europe. It employs 4,500 active-duty military members. They had just arrived In Germany and were on their way to a base when the attack happened.
Frankfurt’s airport is Europe’s third busiest and armed police are a common sight in the airport's lobby. But the shooting took place in a public, nonsecure area just outside one of the two main terminals.
Germany is home to two-thirds of some 75,000 US troops stationed Europe, and Frankfurt's airport is a major transit point for the country's 18 US bases. The airport is also about an hour from the US Air Force's headquarters in Europe, Ramstein Air Force Base, which is often used as a logistical hub for operations in Afghanistan or Iraq.
"It is very distressing, this is my home airport, this is the airport I go in and out of," says a woman married to a US airman who declined to give her name.