BOISE, Idaho -

An Idaho inmate already serving a life sentence for another crime has pleaded guilty to raping and murdering a Boise woman 15 years ago.

The plea came Tuesday in the case of Patrick Jon Zacharias in the death of Kay Lynn Jackson. The victim was 22 years old at the time her body was found near the Boise Greenbelt south of downtown.

Zacharias agreed to plead guilty if prosecutors in turn vowed not to seek the death penalty. Under a plea deal, he will serve a life sentence without parole and waive all appeals.

Boise Police Department detectives investigated the case for 14 years before getting a break when DNA evidence pointed to Zacharias, who had been in prison since 2007 for lewd conduct with a minor.