The murderer is 21 years old which means that he will most likely be tried under juvenile law. Juvenile law means 10 years max in progressive, human Germany but he will get less because he had a hard childhood (refuge in Germany). If he doesn’t kill another one in prison, he will be released after 2/3 of the time.
This guy will be out after six years and live well on social benefits. If he fathers a couple of children with some muslim breeding machine he will live even really well.
He can be prosecuted under US law. FBI is already investigating. Germany is following US legal standards. My guess is the defense attorneys are already filing papers to keep him in Germany and we and Germany are filing papers to get him shipped to the US.