Man, 50, guilty in 1975 cold-case murder

A man who has long been considered a prime suspect in the slaying of his teenage neighbor more than 30 years ago was found guilty Tuesday of second-degree murder.

A King County Superior Court jury heard more than two weeks of testimony and deliberated for three days before finding James Groth guilty of second-degree murder in the February 1975 stabbing death of Diana Peterson, 16.

"Justice was finally done," Senior Deputy Prosecutor Carla Carlstrom said.

Groth and Peterson were classmates at the former Shoreline High School when she was killed. Investigators say he was infatuated with her and was often at the Peterson home in the Richmond Beach neighborhood.

On the night of Feb. 14, 1975, Peterson, a friend and Groth were watching television in the basement of the Peterson home. Peterson's mother agreed to let her daughter go with other friends to a nearby pizza parlor as long as she returned by 10:30 p.m. Groth stayed behind.

Peterson's younger sister testified during the trial that she and her mother were watching television when they heard Peterson in the backyard playfully saying "stop it" and "don't." Their mother, Leanne Peterson, then went to the door and called her elder daughter's name, but got no response.

George Peterson, the slain girl's father, found Diana dead in their backyard the following morning.

Groth, 50, was interviewed hours after the killing and questioned several times in the decades following her death. However, it wasn't until December 2007 that he was arrested by cold-case detectives and then charged with first-degree murder.

Because Peterson was killed before the creation of current state-sentencing guidelines, a Superior Court judge will impose a minimum sentence.

Information from Seattle Times archives is included in this report.

Jennifer Sullivan: 206-464-8294 or jensullivan@seattletimes.com