A Montana man who shot and killed a foreign exchange student for trespassing on his property may have been high and drunk at the time of the incident, CBS News reported.

Markus Kaarma was charged with the April 27 murder of 17-year-old German student Diren Dede, whom he killed with a shotgun in his garage after his motion sensors went off. Kaarma, a 29-year-old firefighter, claims he thought he was in danger. But investigators say that not only did Kaarma set a trap to lure intruders, he was possibly under the influence.

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," Detective Dean Chrestenson said in a statement obtained by CBS News.

Police in Missoula got permission from a judge to test Kaarma to determine if drugs were in his system at the time of the shooting, according to court documents. The results of the test will most likely be kept confidential as the investigation unfolds, CBS News reported.

Police also searched his home and found a jar of marijuana.

Kaarma reportedly told his hairdresser he has been staying up at night to catch trespassers. The firefighter was robbed twice before and wanted to shoot the culprits, prosecutors said.

Kaarma's girlfriend, Janelle Pflager, also told a neighbor that someone stole the marijuana and pot pipes, police said.

Dede, who attended Big Sky High School, entered Kaarma's garage, the door of which was left open the night he died. The sensors went off and the firefighter and his girlfriend saw a figure in the garage on a video monitor. Kaarma fired four shots into the garage without any warning.

Police did not say why Dede was in Kaarma's garage, CBS News reported. Kaarma has been charged with deliberate homicide. He is expected to appear in court May 12.