BILLINGS, Mont. (AP) — A defense attorney says a Wyoming teenager was suffering from insanity when he allegedly shot three people, killing two, on Montana's Crow Indian Reservation.

Federal Defender David Merchant II said in a court filing that Jesus Deniz Mendoza should undergo a competency exam to determine if he is fit to stand trial in the July shootings.

Merchant says Mendoza suffers from an unspecified "severe mental disease or defect" that may have left him unable to appreciate the nature of his actions.

Mendoza, of Worland, turned 19 years old last month. He faces 12 criminal charges including two counts of first degree murder in the deaths of Jason and Tana Shane.

Authorities say the couple and their daughter were shot after stopping to help Mendoza along a roadside near Pryor.