A Montana homeowner may have been high on marijuana or alcohol when he shot dead a German exchange student in a case expected to test the state's "stand your ground" self-defense law, legal documents released Tuesday.

Markus Kaarma, 29, a U.S. Forest Service firefighter, fired his shotgun into his garage in Missoula after midnight on April 27, killing Diren Dede, 17, a student from Hamburg.

Kaarma "may have been impaired by alcohol, dangerous drugs, other drugs, intoxicating substances or a combination of the above at the time of the incident," a Missoula police detective said in a sworn statement.