The 29-year-old shooter, Markus Kaarma of Missoula, Montana, was taken into custody on Sunday after police found the victim with a gunshot wound to his head, police sergeant Travis Welsh said.
"Initial reports indicate that the male resident encountered an intruder in his garage after an alarm went off, and subsequently shot him with a shotgun," Welsh said.
Diren Dede, of Hamburg, Germany, was studying at Big Sky High School in Missoula, where he played for a soccer team.
If convicted, he faces a minimum of 10 years and up to 100 years in state prison. Acting Justice of the Peace Suzanne Geer set bail at $30,000.
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The couple were on their couch, watching television, when an alarm sounded, Ryan said. "They had no choice in their mind other than to confront the intruder," he said.
The lawyer said he expected his client to plead not guilty at the preliminary hearing set for May 12.
He said he would invoke the so-called "Castle Doctrine," under which Montanans have the right to use deadly force to protect their homes if they feel threatened.
In 2012, in a case which sparked local outrage, Montana prosecutors decided not to charge a man who shot and killed another man in his garage.