BOISE — A Utah man already serving a life sentence for murder has pleaded guilty to killing a Boise girl in 1982, closing a case that flustered detectives for decades and was ultimately solved by advances in DNA technology.

In one hearing Monday, Wesley Allan Tuttle, 55, was charged, pleaded guilty and was sentenced to life in prison for first-degree murder in the slaying of 14-year-old Lisa Chambers.

As part of the plea agreement, Ada County prosecutors agreed not to pursue the death penalty, opting instead for a fixed life term.

"Any lesser sentence would depreciate the seriousness of your crime," 4th District Judge Darla Williamson told Tuttle during the 90-minute hearing.

Chambers disappeared Nov. 10, 1982, walking to school, and from the onset Tuttle was considered a person of interest.

Pheasant hunters found her body weeks later, on Thanksgiving Day, frozen in a cornfield near the Western Idaho Fairgrounds. An autopsy concluded she had been sexually assaulted and strangled.

A witness told police about seeing a girl matching Chambers' description near the fairgrounds next to a truck registered to Tuttle. Last fall, Ada County Sheriff Gary Raney said the witness who wrote the license plate down and called in that tip in 1982 has dementia and could not be called on to testify in court.

Even though the girl's path to school passed the neighborhood where Tuttle lived, and Tuttle had recently been released from prison, Raney said detectives dismissed the tip after failing to find that Tuttle had any connection to her family and because the reported sighting was so far from where she lived.

For years, detectives made a point of revisiting the case and kept an 8-by-10-inch school photo of Chambers posted in the bureau. At least three detectives who worked the case have since retired, leaving the case file for younger colleagues.

"It's important that justice was served today," said Ron Freeman, chief deputy for the Ada County Sheriff's Office.

The biggest break emerged from legal changes in the last 15 years that have allowed state and federal authorities to collect DNA from convicted felons and the collection of that genetic information in a national database, officials said. At the time his saliva was collected, Tuttle was being held in a Montana prison for security reasons after escaping a Utah facility in 1991.

Then in March 2007, Ada County detectives submitted a DNA sample taken from Chambers' underwear to the state crime lab, which matched it to Tuttle's sample in the database. Prosecutors then traveled to Utah to obtain a blood sample from Tuttle, which confirmed Tuttle's link to the slaying and prompted negotiations between prosecutors and Tuttle's lawyer.

"We were engaged in negotiations for almost a year on this," said Ada County Prosecutor Greg H. Bower, who was first elected to the job just days before Chambers' disappearance.

"Justice was done for two major reasons. The men and women of the sheriff's department never gave up. And technology caught up to Wesley Tuttle," Bower said.

Tuttle, wearing a blue dress shirt and tan dress pants, offered little explanation during the hearing.

With prodding from the judge, the former long-distance trucker who said his education level is no higher than the fifth grade shared a few details of the crime. At one point, he said he had no idea why he killed the girl, but later suggested he acted out of "rage and anger."

Tuttle was also convicted and sentenced to life in prison for the 1983 killing of 21-year-old Sydney Anne Merrick, who was stabbed to death along a Utah highway.

Nancy Chapman, Chambers' mother, did not attend Monday's hearing, but issued a statement thanking detectives.

"The next time I go to the cemetery, I can tell my daughter, 'We found your killer. You can rest in peace,"' she said.