HELENA, Mont. - A Montana man has been sentenced to 70 years in prison, with no parole for at least 20 years, in the shotgun killing of a German exchange student who was trespassing in his garage.

Markus Kaarma, left, enters Missoula County District Court in Missoula, Montana, May 21,2014. REUTERS/Arthur Mouratidis

Markus Kaarma was sentenced Thursday after a Missoula jury convicted him in December of deliberate homicide in the shooting of 17-year-old Diren Dede.

The case caused an outcry in Germany and brought scrutiny to Montana's "castle doctrine" law that can allow the use of deadly force to protect home and family.

Kaarma shot the unarmed teenager in April after he was alerted by motion sensors in his garage. Witnesses testified that Kaarma fired four times.

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Prosecutors argued Kaarma was intent on luring an intruder into his garage after it had had been burglarized at least once in the weeks before the shooting. Three witnesses testified they had heard Kaarma say he'd been waiting up nights to shoot an intruder.

Kaarma's lawyers argued the Missoula man feared for his life, didn't know if the intruder was armed, and was on edge because of a previous burglary.

They also argued Montana law -- the so-called "castle doctrine" -- allowed the 30-year-old Kaarma to use deadly force to defend his home.

They've said they'll appeal his conviction.