INDIO, Calif. -

An already condemned child killer pleaded guilty today to the 1997 kidnap-murder of a 10-year-old Beaumont boy and is expected to be sentenced to life in prison without the possibility of parole, avoiding another death sentence.

Joseph Edward Duncan III, 48, has already been sentenced to death for the killings of an Idaho boy and three members of his family. He could have faced the same fate had he been convicted at trial of killing the Coachella Valley youngster.

Defense attorneys proposed a deal in February calling for Duncan to plead guilty to Anthony Martinez's murder in exchange for a life prison term, but prosecutors did not immediately agree to the deal. Last week, they asked for more time to consider the proposal and, with District Attorney Paul Zellerbach's approval, accepted it today at the Larson Justice Center.

"I've never seen a person in my professional career who deserves the death penalty more than Joseph Duncan," Zellerbach said during a news briefing at the D.A.'s headquarters in downtown Riverside this afternoon.

The former judge said he wouldn't have considered a plea agreement with Duncan if the convicted child killer hadn't already been sentenced to death in federal court for the Idaho boy's murder.

"As a prosecutor, I handled 50 murder cases and 35 death penalty cases. I presided as a judge over seven death cases and sentenced five people to death. I've sentenced some of the worst of the worst child killers, and Mr. Duncan ranks right up there in the top three," Zellerbach said.

He said Anthony's family favored a life sentence for Duncan to bring a conclusion to the case.

The child's mother told reporters she "didn't want to wait any longer" for a resolution.

"I've waited 14 years to fall apart," Diana Gonzalez said tearfully. "He's convicted. We're ready for it to be done."

Zellerbach said he expected Duncan would be executed for the Idaho murders "in the next few years."

The defendant is slated for formal sentencing in the Martinez case on April 5.

Beaumont Police Close Martinez Case

As the plea agreement was made official in court, Beaumont police closed the murder case of Martinez.

"We are relieved that Anthony's family and the entire community, as well as those who were involved in the search for Anthony, can finally find closure," said Police Chief Frank Coe. "The person responsible for the kidnapping and murder of a young, innocent child will face justice and never have the opportunity to commit another brutal crime."

Martinez's murder still haunted one of the lead investigators on the case.

Mitch White retired from the Beaumont Police Department after Duncan was arrested.

"I have waited almost fourteen years for the day that the killer of Anthony Martinez would face justice and today is that day," he said. "The case is now closed and I hope that those that have been so deeply affected be this tragedy can finally have the peace they deserve."