Amber Alert Manhunt Expanded After Possible Sighting

James Lee DiMaggio is suspected of killing Christina Anderson, abducting her children.
2:36 | 08/10/13

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Transcript for Amber Alert Manhunt Expanded After Possible Sighting
Well it turned a major development this morning in the intense all out manhunt for a San Diego murder suspect ended teenage girl he's believed to have kidnapped his car was found -- a remote location in Idaho now the two were spotted by a man on horseback. ABC's -- -- -- -- San Diego with the latest on the Sargent -- if there's any good news of this man says seems to say that the girl was alive the sixteen year old who he believes is this victim. So far beyond -- yes that's what they believe and it's a positive development. An overnight sad development police positively identified the remains of eight year old Ethan Anderson. Who was murdered here in San Diego but right now and Idaho search teams are looking for his suspected killer. Who they believe also kidnapped. You -- sister. This morning over 100 federal agents and police are swarming this Idaho wilderness hunting for a murder suspect and a teenage -- they believe is in grave danger. It's treacherous terrain it is and he is back country you know it is wilderness and so we're gonna bring in any resources that we can. On the ground and from the air to make this -- the successful. They're here because a man on horseback says he crossed paths with two people Wednesday believed to be forty year old -- DiMaggio and -- Eighteen year old Hannah Anderson they did appear to have gear with them they had. Camping equipment it seemed to hand. I think he describe the interaction as odd but nothing alarming. Nothing alarming until the horseback rider recognize tennis photo on the news and called police. DiMaggio whose car was found Friday a few miles away hidden under bushes the license plates missing. They checked the vehicle identification number through the windshield. And confirm that it was indeed are suspect vehicle from San Diego. Police had warned it might be booby trapped with explosives but none were found. Police believe DiMaggio killed -- his eight year old brother Ethan and their mother Christina last Sunday at his house outside San Diego setting it on fire. Kidnapping the girl investigators say DiMaggio was a family friend who had an -- usual infatuation with Hannah. Overnight in their hometown of lakeside California Hannah and -- whose father spoke at a candlelight vigil. It's great that we travelers -- -- days. And we hope that everything has been going well -- -- home. Now they search area is massive more than 300 square miles but this morning investigators from here in San Diego County will be joining the search effort. They'll be looking on foot on horseback. And from the air Dan. Hopefully this nightmare will end soon Clayton thank you.

This transcript has been automatically generated and may not be 100% accurate.

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