Image copyright AP Image caption The shooting took place on Crow Indian Reservation in Montana

An 18-year-old man has been arrested after police say he shot and killed two people who stopped to help him along a road in a Montana Indian reservation.

Tana Shane saw Jesus Deniz stranded without fuel on the side of the road on Wednesday near her home.

But when she returned to help with her husband and daughter, Mr Deniz robbed and shot them, killing the couple and wounding their daughter, police said.

Mr Deniz shot them after the daughter laughed at him, police said.

Mr Deniz fled in the Shanes' car, but he was apprehended in Meeteetse, Wyoming, about 120 miles (190 km) away from Pryor, the small town on the Crow Indian Reservation where the shooting took place.

He is expected to be returned to Montana for a court appearance on Friday.

The daughter, 26-year-old Jorah Shane, underwent surgery on Wednesday to remove a bullet from her spine, but she is expected to survive.

"He's only 18, and he looked like an innocent boy," said Ada Shane, a relative of the victims. "Both my brother and sister-in-law have big hearts."