Diren Dede, 17, was shot dead on Sunday in the garage of Markus Kaarma in Missoula, Montana.
Kaarma, 29, was charged with murder on Monday and his lawyer Paul Ryan said on Wednesday his client has since received death threats.
The lawyer said Kaarma saw Diren in the garage on Sunday night and felt “threatened”.
Ryan said: “They didn’t know what he wanted in the garage, how he would act.”
A spokeswoman for Hamburg’s state prosecutor said they too would investigate the death. “We are checking the facts and have already requested documents from the American authorities,” she said. German law also applies for crimes committed against Germans abroad.
Diren, whose family is originally from Turkey, was taken to hospital but died from a gunshot wound to his head.
His body is expected to be flown to Turkey to be buried, his football trainer confirmed on Wednesday.
The teenager’s father, meanwhile, has flown to the USA to bring back the body of his son.
Diren moved to Montana, last August for a year abroad.
He was a keen footballer and played for SC Teutonia 1910 in Hamburg. The club is holding a game on Wednesday night in his memory and will collect funds for his family.
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