LOS ANGELES (CBSLA) – A 60-year-old man already serving prison time for an unrelated murder was convicted earlier this week in the brutal cold case killing of a 36-year-old woman in her Silver Lake apartment nearly four decades ago.

Harold Anthony Parkinson was convicted Tuesday by a Los Angeles County jury of one count of first-degree murder in the 1980 slaying of Stephanie Sommers, according to the L.A. County District Attorney’s Office. The jury also determined that Parkinson had raped her.

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On Aug. 30, 1980, Sommers was raped and stabbed to death 16 times in her apartment in the 3500 block of Marathon Street. She was also bludgeoned in the head with an eight-pound weight.

The case went unsolved until cold case L.A. police detectives got a lead that Parkinson — who had lived a mile away from the victim — could be a suspect in the killing.

A DNA sample collected from Parkinson was consistent with the DNA profile from a sperm sample collected from Sommers.

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Stephanie Sommers in an undated photo (credit: CBS)

Parkinson is already serving 15 years to life in prison for a 1981 murder which also occurred in L.A. He has been in prison since March of 1982.

Prosecutors opted not to seek the death penalty. He now faces life in prison without the possibility of parole when he is sentenced on the new conviction on Dec. 2.

He is currently housed at the Chuckawalla Valley State Prison in Riverside County.

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(© Copyright 2019 CBS Broadcasting Inc. All Rights Reserved. City News Service contributed to this report.)