The terrorist-style killings were the first by an Islamist on German soil. Prosecutors will argue that Kosovo-born Arid Uka acted alone and was not a member of any terrorist group.
“What the indictment accuses me of is correct,” Uka said after the indictment was read out. “I wanted to kill the soldiers.”
He said he began to think after the killing that what he had done had been stupid.
Security was strict at the trial in Frankfurt’s state superior court.
To ensure a murder conviction, prosecutors will focus at the trial, set to run into next year, on Uka's alleged motive: to advance the Islamist cause by attacking any American military personnel.
Prosecutors say the victims were chosen because they were on their way to tours of duty in Afghanistan.
Charges of terrorism have not been laid because there was no evidence that Uka belonged to any group.
Uka reportedly told police that he followed two men in uniform to a waiting US Air Force bus, where 16 unarmed servicemen who had just arrived from London were loading their bags for a road trip to an airbase.
Investigators say he shot dead one man, 25, in the back of the head outside the bus, then killed the 21-year-old bus driver. They say he then critically wounded two, aged 21 and 25. One of them was permanently blinded in one eye.
His pistol jammed as he aimed at another man, 22, police say. He was then caught by police and an air force soldier. – Sapa-DPA