By Marty Graham

SAN DIEGO (Reuters) - Police and federal agents in Southern California widened their manhunt on Wednesday for a computer technician who is suspected in the slaying of a longtime friend, the disappearance of her two children and the arson fire of his own home.

The fugitive, James Lee DiMaggio, 40, had been a close family friend of Christina Anderson for two decades and was "like an uncle" to her children, said Lieutenant Glenn Giannantonio, the homicide detective overseeing the case for the San Diego County Sheriff's Department.

Investigators have no evidence of a precipitating incident or circumstances that might have led to the crimes DiMaggio is suspected of committing, the detective said on Wednesday.

Anderson, 44, and her two children - 16-year-old Hannah and 8-year-old Ethan - were last seen Saturday evening, he said.

The following night, the mother was found slain inside DiMaggio's burned-out home in the desert community of Boulevard, California, east of San Diego, along with a dead child whose remains were burned beyond recognition.

Authorities have not said how the mother was killed.

Giannantonio said it might take a day or two longer for medical examiners to positively identify the child and determine the cause of death. But investigators believe the remains, which are consistent with those of an 8-year-old, may belong to Ethan Anderson, he said.

At this point, he said, there is no other child of that age whom investigators have linked to the case. But for now, investigators have not ruled out the possibility that DiMaggio abducted both Hannah and Ethan Anderson.

"We know we're missing an 8-year-old and a 16-year-old," Giannantonio said.

Anderson's ex-husband and the children's father, Brett Anderson, went on television on Tuesday night to make a public plea to the suspect to give himself up and for his daughter to try to escape.

"Jim, I can't fathom what you were thinking," he said. "The damage is done. I'm begging you to let my daughter go. You've taken everything else."

He also addressed the missing girl, saying, "Hannah, we all love you very much," adding, "If you have a chance you take it. You run. You'll be found."

A statewide child-abduction notice, or Amber Alert, was issued Monday night for both children, and authorities said DiMaggio was initially believed to be headed by car for Texas or Canada.

On Wednesday, however, Giannantonio said investigators had no clue as to the suspect's intended destination. He said FBI agents have joined in the search, and that Mexican law enforcement authorities and the U.S. Border Patrol also were on the lookout for DiMaggio.

"It's very possible he could be hunkered down somewhere here in the county," the detective told Reuters. "He's something of an outdoorsman. He could be somewhere around here camping."

Giannantonio said there has been no communication from DiMaggio, who made a living as an information technology worker, since he disappeared.

DiMaggio had been a friend of Brett and Christina Anderson for about 20 years, and he remained close to Christina, though they were not romantically involved, after the couple divorced and the husband moved to Tennessee, Giannantonio said.

"This kids considered him like an uncle, and he considered them like a niece and nephew," the lieutenant said.

(Reporting by Marty Graham; Writing and additional reporting by Steve Gorman; Editing by Cynthia Johnston and Cynthia Osterman)