Officials have confirmed that the burned body found in a California house is that of an eight-year-old boy whose sister is the subject of a massive search in the Idaho wilderness.

Police on Friday night positively identified the victim as Ethan Anderson, who was listed as missing.

The burned bodies of the boy and his mother, 44-year-old Christina Anderson, were discovered last Sunday in a log-style cabin in Boulevard, Calif., just east of San Diego last Sunday.

The burned-out home belonged to 40-year-old James Lee DiMaggio, who authorities believe abducted the woman's daughter, 16-year-old Hanna Anderson.

Investigators had to identify Ethan's body through DNA extraction from his bone marrow.

Authorities are now focusing on Idaho in their search for the girl and the man suspected of killing the teen's mother and brother.

A horseback rider had reported seeing two people matching the pair's descriptions in the Cascade area northeast of Boise.

On Friday morning, a car belonging to DiMaggio was found covered in brush in the backcountry of Idaho's Valley County.

Police are worried the teen and DiMaggio are in what has been described as the largest roadless area in the lower 48 states.

The search area is bisected by a waterway that winds through steep canyons and dense forests.

Away from the river, it's easy to disappear, said Jared Hopkinson, the owner of Rocky Mountain River Tours in Stanley, Idaho.

Hopkinson said a backpacker can hike for days without seeing another person.

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  • James Lee Dimaggio Manhunt

    FILE - This composite photo provided by the San Diego Sheriff's Department shows: James Lee Dimaggio, 40, left, Ethan Anderson, 8, and Hannah Anderson, 16, whose mother, Christina Anderson, 44, was one of two people found dead in a house fire Sunday night, Aug. 4, 2013. Amber Alerts expanded to Oregon and Washington as authorities searched for Dimaggio, who is suspected of abducting Hannah Anderson and wanted in the death of the girl's mother and possibly her brother Ethan. (AP Photo/San Diego Sheriff's Department, File)

  • James Lee Dimaggio Manhunt

    This photo provided by the San Diego Sheriff's Department shows James Lee Dimaggio, 40, who is suspected of killing Christina Anderson, 44, who was one of two people found dead in a house fire Sunday night. An Amber Alert was in effect early Tuesday Aug. 6,2013 for two missing children Ethan Anderson, 8, and Hannah Anderson, 16, children of Christina Anderson, whose body was found inside a burned rural house near the U.S.-Mexico border, and authorities said Dimaggio, suspected of killing the woman may have abducted the kids. (AP Photo/San Diego Sheriff's Department )

  • James Lee Dimaggio Manhunt

    Brett Anderson, the father of missing children 16-year-old Hannah Anderson and 8-year-old Ethan Anderson, arrives to a news conference Tuesday, Aug. 6, 2013, in San Diego. Anderson, the husband of a Christina Anderson, whose body was found in a burned house near the U.S.-Mexico border, said Tuesday that he knew the man suspected of killing his wife and abducting one or both of their children. (AP Photo/Gregory Bull)

  • James Lee Dimaggio Manhunt

    Brett Anderson, the father of missing children 16-year-old Hannah Anderson and 8-year-old Ethan Anderson, speaks during a news conference Tuesday, Aug. 6, 2013, in San Diego. Anderson, the husband of a Christina Anderson, whose body was found in a burned house near the U.S.-Mexico border, said Tuesday that he knew the man suspected of killing his wife and abducting one or both of their children. (AP Photo/Gregory Bull)