San Diego (CNN) -- An Amber Alert has been issued in Oregon for a 16-year-old girl and an 8-year-old boy believed to have been abducted by James DiMaggio, who authorities suspect kidnapped the children after their mother's body was found in his burned-down house in San Diego, the Oregon State Police said Wednesday.
The alert was broadcast after a possible sighting Wednesday afternoon of a vehicle wanted in connection with the case, police said.
A spokeswoman in San Diego later said the tip didn't pan out, but Lt. Gregg Hastings with the Oregon State Police said he hadn't heard that.
"We are not turning our back to this and we are doing what we can to locate that suspect vehicle and the missing children," he said.
An arrest warrant for murder has been issued for DiMaggio. In the event of his arrest, a judge has signed off on a $1 million bond, said San Diego County Superior Court spokeswoman Karen Dalton.
Also found in the home were charred human remains consistent with those of an 8-year-old child, a law enforcement source with knowledge of the investigation said Wednesday.
Police are awaiting DNA tests to confirm whether the remains are of the missing boy, police said.
A San Diego County sheriff's detective previously had said the remains could be those of Ethan Anderson, one of two children for whom the Amber Alert was issued.
Meanwhile, Ethan's father made a public plea Tuesday to the suspect, who is believed to have abducted the boy's sister, Hannah. The father asked DiMaggio to release Hannah, who along with Ethan went missing after their mother was killed.
A massive manhunt is under way for DiMaggio, 40, whom law enforcement authorities describe as a friend of the mother, Christina Anderson.
DiMaggio was the owner and sole resident of the burned home where Anderson's body and the remains of the child were found.
"Jim, I can't fathom what you were thinking. The damage is done. I'm begging you to let my daughter go. You've taken everything else," Brett Anderson, the children's father, said in an appearance before reporters.
"Hannah, we all love you very much. If you have a chance, you take it, you run. You'll be found," he said.
The father did not mention Ethan in his remarks, prompting a reporter to ask San Diego County Sheriff's Department Lt. Glenn Giannantonio whether the remains of the child found in the house might be those of the boy.
"We don't know who that is that was found in the rubble. It is a possibility that it's Ethan. It's a possibility that's another child that we haven't identified yet, or don't realize is missing yet," Giannantonio said.
"Right now, we just don't know, and we're praying that it wasn't Ethan," he said.
Authorities are following up on tips and casting a wide net for DiMaggio and the children.
"We've received some information that either Texas or Canada may have been the destination he was heading to. Realistically, we don't know where they're going," Giannantonio said. "We're looking everywhere."
The remains of Anderson, of Lakeside, California, were found while firefighters extinguished a blaze that broke out at DiMaggio's home in the enclave of Boulevard around 8 p.m. Sunday.
Authorities believe she was killed. Her mother, Sara Britt, said Christina Anderson was 44 years old, not 42 as earlier reported.
Hannah Anderson was last seen at 3 p.m. Saturday at cheerleading practice, according to Britt and her other daughter, Jennifer Willis. Ethan was supposed to be at football practice at 8 a.m. Sunday but never showed, the two relatives said.
DiMaggio was like an uncle to the family, but he was having financial problems, the two relatives said.
"We know that they were lifelong friends. We're not exactly sure what that relationship was. We don't know if Hannah's with him willingly or not. We just don't know right now," San Diego County Sheriff Bill Gore told CNN's Anderson Cooper 360 on Wednesday.
California authorities also issued an Amber Alert. Once they did, information was distributed to residents' cell phones statewide through the Wireless Emergency Alert program, according to the California Highway Patrol.
The wireless program was instituted in December 2012, and this was the first time it had been used statewide, CHP Public Information Officer Erin Komatsubara told HLN.
On HLN's "Raising America" on Tuesday, the children's aunt, Andrea Saincome, said that DiMaggio had known the family for years and that it would not have been unusual for the mother and children to be at his house.
"There was nothing out of the ordinary," Saincome told HLN's Christi Paul. "He seemed like a genuinely nice guy. He was close to the kids, and he was friends with my sister and my brother-in-law."
The children were reported missing by their grandparents on Sunday. Giannantonio said he did not know what led them to believe their grandchildren were missing.
Giannantonio would not release any details about how Anderson was killed, but said arson investigators believe they know how the fire was started. Authorities also found burned weapons in the residence.
The sheriff's office released several photos of DiMaggio, and Giannantonio said he was believed to be driving a blue, four-door Nissan Versa with California license plate 6WCU986.
However, he might have switched vehicles, taken public transportation or be hunkered down somewhere, Giannantonio said.
He asked for the public's help, as did Gore.
"We need all the eyes and ears out there we can get in trying to find both DiMaggio and hopefully those two kids," the sheriff said. "Citizens should not try to interfere with this person at all. He's already proven he's a pretty dangerous fella."
Anyone with information about the case is asked to call the San Diego County Sheriff's Department Homicide Detail at 858-974-2321 or submit an anonymous tip to Crime Stoppers at 888-580-8477.
HLN's Steve Loiaconi and CNN's Paul Vercammen contributed to this report.