Registered sex offender John Albert Gardner III is under investigation for the killing of Amber Dubois, the Escondido teen who disappeared 13 months ago and whose remains were discovered Saturday near the Pala Indian Reservation, police said Monday.

"The Amber Dubois crime scene is still being processed and John Albert Gardner III remains a focus of the investigation," Escondido police Lt. Craig Carter said in a prepared statement.

Gardner was charged Wednesday with murder in the commission of a rape or attempted rape in the killing of Chelsea King, 17, of Poway. Chelsea was reported missing Feb. 25; a body believed to be Chelsea's was discovered March 2 in a shallow grave in the Lake Hodges area.

Gardner has pleaded not guilty.

Amber's remains were found early Saturday after what police have described only as a "lead" in their investigation.

"They would be derelict not to consider (Gardner) in this investigation," said Kerry Steigerwalt, a prominent San Diego defense attorney. "Let's give the police the time they need to make the case as solidly as they can make it."

Steigerwalt said it's unlikely that Gardner gave police information on Amber's case because his defense attorneys would have advised him against talking to investigators.

Gardner's attorney, Deputy Public Defender Michael Popkins, declined to comment on the latest police statement.

The 30-year-old Gardner has pleaded not guilty to the charges in the Chelsea King case.

He is due to appear Tuesday morning in San Diego County Superior Court for a scheduled status conference with defense attorneys and prosecutors.

Gardner lived in Escondido from January 2008 to January 2010.

Police said they contacted him eight times during that period and began a fresh look at him and any possible ties to Amber after his arrest in connection with Chelsea's killing.

Police released no further details Monday about the information that led them to Saturday's discovery.

It was unclear whether the Chelsea King investigation led authorities to Amber's remains, more than a year after the 14-year-old disappeared while walking to Escondido High School.

Riverside County sheriff's officials said Monday that they are continuing to investigate whether Gardner is connected to an attempted abduction in October of a Lake Elsinore girl.

Gardner registered his address in Lakeland Village, just outside Lake Elsinore, in early January.

Riverside County authorities also are investigating whether Gardner is connected to any sexual assaults or missing persons cases in the area.

But he is not labeled a "suspect" in any case, sheriff's Sgt. Joseph Borja said.

On Monday, Michelle Bart, a spokeswoman for Amber's maternal grandmother, Sheila Welch, said she and Welch are questioning why it took police until Saturday to find Amber when specially trained private search dogs picked up her scent in the same Pala area in August.

Search for clues continues

Law enforcement teams continued to scour a scrubby, rocky hillside west of Pala Temecula Road, about three miles north of Highway 76, where Amber's body was found.

Two officers guarded the single-lane road that leads up the hillside from Pala Temecula Road.

At the Pala Indian Reservation, a small group of men were talking Monday morning outside a grocery store about the discovery of Amber's remains near their small community.

All of them said they were upset that some news organizations had reported that the body had been found on the reservation.

"We don't like it because they say Pala," said Alan Majado, 59, a resident of the reservation.

Majado added that the reports make Pala sound like a "dumping ground."

In 1991, the remains of 7-year-old Leticia Hernandez, who had been missing from her Oceanside home for 15 months, were discovered in a remote canyon about three miles south of the Riverside County line near the reservation.

Gardner would have been 9 years old at the time of her disappearance.

The August effort

Amber was 14 when she was reported missing Feb. 13, 2009.

After months of investigation turned up no viable leads, Maine's VK9 Scent Specific Search Recovery offered the services of its dogs in August.

Welch paid the team's expenses.

Handler Julie Jones said the two Labrador retrievers used in that search effort have a proven ability to track an old scent trail, even if the missing person has traveled in a car.

For three days, the two handlers, Bart, an Escondido police officer and a private investigator Welch hired followed the dogs.

Both dogs picked up Amber's scent at her north Escondido home and followed it to Interstate 15, Jones said.

The animals and their handlers walked part of the way, Jones said.

When it was clear they were following a freeway, they traveled by car.

At off-ramps, the dogs were let out to test whether the trail continued north, Jones said.

At Highway 76, the dogs picked up Amber's scent and headed steadily toward Pala, Jones said.

Around the Pala Mission, and for approximately three miles north on Pala Temecula Road, the dogs found Amber's scent in numerous locations, the handler said.

In the area Amber's remains were found, the dogs again followed a trail, Jones said.

"Our reports are that we could not find any exit trail for Amber in the Pala area, so it either meant to us she is alive and she's there, or that she's there but no longer alive," Jones said.

Bart said the dogs' response amazed her, and she submitted a report to Escondido police describing the dogs' unequivocal path.

"The dogs were going crazy," she said. "Where they really went nuts was in the residential area across the street from the casino."

Jones said the dogs did not indicate a scent trail anywhere else.

The search team briefed Escondido detectives, emphasizing their belief that Amber was still in the Pala area.

But Jones acknowledged that traditional search and rescue experts are often skeptical of the dogs' abilities.

'Brazen claim'

Bart said family members wonder whether police ever followed up.

In September, Amber's parents, Maurice Dubois and Carrie McGonigle, who are long separated, accused police of "dropping the ball" in following the Pala leads.

It was not clear Monday whether they still hold that opinion.

However, Dave Cave, who lived with McGonigle and helped raise Amber for years before her disappearance, said it's too early to question whether police properly followed up on tips in Pala.

"I don't have enough facts to feel anything (about the job they did in Pala) and neither does Sheila or anyone else," Cave said.

In September, Lt. Bob Benton defended the department's response to the private search reports, noting that an Escondido police officer accompanied the search team in Pala.

Michael Boyle, an Orange County Fire Authority battalion chief who worked with search dogs as part of a multi-agency search and rescue task force for almost 20 years, called it a "pretty brazen claim" that dogs could follow a 6-month-old outdoor trail.

"There are so many variables" that can degrade a scent trail, even for the most sensitive dogs, Boyle said. "Hopefully, it doesn't rain and the wind doesn't blow."

Staff writer Chris Nichols contributed to this report.