(CNN) -- The national manhunt for California Amber Alert suspect James DiMaggio and his alleged 16-year-old captive girl has moved to the Idaho wilderness after horseback riders saw a man and a girl fitting their description, authorities said Friday.
Investigators subsequently found DiMaggio's car hidden by brush, with its license plates removed, San Diego County Sheriff Bill Gore told reporters. Authorities confirmed the car's ownership by its vehicle identification number, he said.
The vehicle was located in the remote River of No Return Wilderness area in Cascade, Idaho, Ada County sheriff's spokeswoman Andrea Dearden said.
Not aware of the manhunt at the time, the campers and hikers on horseback saw the man and girl Wednesday, but they called police after they saw news account that evening, police said.
"It is a wilderness and extremely difficult terrain to navigate," Gore said.
The vehicle will be examined by bomb and arson technicians to ensure it's not rigged with explosives, Gore added.
The horseback riders observed the woman -- believed to be 16-year-old Hannah Anderson, whom DiMaggio, 40, has allegedly kidnapped -- to be in good condition, Gore said.
"They both appeared to be in good health," Gore said.
The man and woman sighted by the campers were carrying backpacks, with a tent, about six miles outside Cascade, Idaho, Gore said.
Meanwhile, authorities continued Friday to deem DiMaggio a dangerous suspect because he is accused of killing the girl's mother and possibly the woman's son.
A search of the burned-down house belonging to DiMaggio has led law enforcement to this conclusion: "We don't hold anything past this person," as one official put it.
Authorities found the body of Hannah Anderson's mother, Christina, in DiMaggio's San Diego-area home, and a second body likely to be Christina Anderson's 8-year-old son, Ethan.
Details of what investigators have uncovered at the scene remain under wraps, but it has led authorities to warn that the suspect's car may be rigged with explosives.
"We have a heightened concern that's based on the evidence we have been collecting at the scene all week long," San Diego Sheriff's Department Capt. Duncan Fraser told CNN Friday.
"We think that he's capable of anything at this point," he said.
Based on what the sheriff's investigators have seen, there is evidence that the fire and kidnapping of Hannah was a "very well planned event," Fraser said.
On Friday, Idaho joined the list of states that have issued an Amber Alert for the missing teen and the suspected child kidnapper.
Four other states -- California, Oregon, Washington and Nevada -- had previously issued Amber Alerts.
DiMaggio is a camper, so it is possible that he is hunkered down somewhere in a rural area, the San Diego Sheriff's Department said.
The manhunt has been ongoing all week, and authorities have been counting on the public for clues that may lead them to DiMaggio.
"We've got law enforcement agencies across the country looking for them and following up on tips that are being called in," San Diego County Sheriff's Department Lt. Glenn Giannantonio told CNN on Thursday. "We've received numerous tips, I'd say probably well over 100, possibly hundreds of tips from across the country. Every tip that can be followed up on has been followed up on or is currently being followed up on."
It is also possible DiMaggio has abandoned his car and left it rigged with explosives, sheriff's spokeswoman Jan Caldwell said Thursday.
Fraser didn't elaborate on Friday, except to say that evidence at the burned house indicates that there are explosives.
Suspect is family friend
DiMaggio was described as being so close to the family whose life he allegedly turned upside down that he was considered part of it.
He came into the lives of Brett and Christina Anderson months before their daughter, Hannah, was born.
"He basically became part of our family," Brett Anderson told CNN's Chris Cuomo on Thursday.
DiMaggio was such good friends with the family that Anderson said he can't reconcile the man he knows with the crimes he is suspected of.
"I have been through every scenario in my brain," Anderson said. "There was nothing ever to show any indication of this."
DiMaggio joined the family on campouts and was always friendly toward them, he said.
"I can't fathom what happened in Jim's head. He obviously just lost it," Anderson said.
"You've taken everything," the father pleaded to DiMaggio in the interview. "The damage is done. Just let my daughter go, Let her go home safe, let her be with me and try to mend things from there."
Some witnesses have told investigators that DiMaggio had a crush on Hannah, but Brett Anderson has said the family had no knowledge of that.
Fraser said that they are looking into whether the suspect possibly had an "undue infatuation" with the teen.
Awaiting ID of remains
The remains of Christina Anderson, of Lakeside, California, were found while firefighters extinguished the blaze that broke out at DiMaggio's home in the enclave of Boulevard around 8 p.m. Sunday.
In addition to her body, charred remains consistent with those of an 8-year-old child were found, authorities said. The remains were so badly burned that carrying out a DNA test is proving difficult.
It is possible that the remains are those of Ethan, but until there is a positive identification, the sheriff's office is treating him as a missing person.
CNN's Paul Vercammen, Miguel Marquez and HLN's Katherine Cavazini contributed to this report.