Jon Meyer Jr. told police in Grants Pass, Ore., that he was using his assault rifle as a crutch when it accidentally fired and killed a little girl in the room above on June 27.
According to the Associated Press, Meyer was charged with manslaughter, assault and unlawful possession of a machine gun. He is being held on $250,000 bail.
The little girl, Alysa Bobbitt, and her mother, Danielle Wilson, were upstairs in the same apartment that Meyer was in.
When the gun went off, bullets fired through the ceiling killing Bobbitt and wounding resident Karen Hancock, who was also upstairs.
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After a 911 call was made, police and firefighters tried to treat the 5-year-old girl's gunshot wounds, and then rushed her to Three Rivers Hospital where she died, notes Q13Fox.com.
It is not clear what exactly Meyer was doing in the apartment.
Meyer's fiancee, Victoria Kohout, filed for a restraining order on June 20 and described him as an "unpredictable drug addict" who had threatened her with a gun.
Sources: Associated Press and Q13Fox.com