Investigators said Tuesday they believe the same man who fatally shot a New Hampshire couple near a scenic northern Arizona resort town also killed a sheriff's deputy several days later in Phoenix.

Ballistics experts confirmed that the rifle casings found at the scene near Sedona on Friday and in the parking lot of a Phoenix medical building on Sunday came from the assault rifle used by Drew Ryan Maras, Maricopa County Sheriff Joe Arpaio said.

Arpaio described Maras as a U.S. Marine Corps reservist who briefly attended Arizona State University, recently lost his maintenance job in nearby Peoria and was living out of his van.

The 30-year-old may have been depressed, had lost contact with his family, believed the world was going to end this year and showed an interest in UFOs, the sheriff said.

The deaths of the New Hampshire couple had baffled authorities over the weekend. The bodies of James Johnson of Jaffrey, N.H., and Carol Raynsford of Nelson, N.H., were found in a sedan at a remote highway turnout. Investigators said they found six shell casings on one side of the car, and two on the other side.

Johnson and Raynsford frequently hiked and camped together and were in the area to look for a house for Johnson, said Raynsford's friend, Jayne Kelly. They had planned to head home at the end of the month

Investigators still don't know why they were targeted. Officials have said there was no evidence that the two were robbed or that they had provoked the shooter.

"I don't think we will ever know the motive," Yavapai County Sheriff Scott Mascher said.

Maras fatally shot sheriff's Deputy William Coleman on Sunday after the officer responded to a burglary call at the medical building, Arpaio said.

Coleman knocked on Maras' van to rouse him. Maras responded by opening the vehicle's sliding door and firing 29 shots, authorities said. Other deputies got off 41 rounds and killed Maras.

By Monday, investigators had begun to draw a connection between the two shootings, which took place 85 miles away from each other.

Maras used a variant of an AR-15 assault rifle and shot unique military grade ammunition that has a steel core, giving the slug more penetrating power, investigators said.

He served with the Marine from 1999 to 2003, completing infantry training with a specialty as a rifleman before joining a reserve unit in Chicago, Marine Maj. Shawn Haney said.

Authorities said he had no serious criminal violations. A search of Arizona court records showed just a 2004 citation for driving with a suspended license. But that case was dismissed.

Coleman, 50, was a 20-year veteran. He is survived by a wife and two young children, ages 4 and 7. He also has grown children in another state. He was assigned as a patrol deputy and had previously worked the sheriff's lake patrol unit.

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Associated Press writers Felicia Fonseca in Flagstaff, Ariz., and Kathy McCormack in Concord, N.H., contributed to this report.