Story highlights The family stopped to help Jesus Deniz Mendoza, the FBI says

Mendoza said he killed them because they took too long to return, court documents say

(CNN) Trying to be good Samaritans cost two members of a Montana family their lives and left their daughter wounded.

The triple shooting happened in the town of Pryor, Montana, about 30 miles south of Billings.

The suspect, 18-year-old Jesus Deniz Mendoza, is expected in federal court Friday.

The shooting

The family was shot when they returned to help Mendoza, whose car was seen stopped along side a road on the Crow Indian Reservation on Wednesday morning, according to an FBI criminal complaint.

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