SAN RAFAEL (CBS SF) – One of the three defendants charged with killing a Canadian tourist in San Francisco’s Golden Gate Park and a yoga instructor on a Marin County trail pleaded guilty Monday in a plea bargain agreement.

Marin County District Attorney Ed Berberian said that Sean Angold pleaded guilty to one count of second-degree murder and will also testify against his co-defendants – 23-year-old Morrison Lampley and 19-year-old Lila Alligood.

If found guilty, Lampley and Alligood could be sentenced to life in prison without parole. The Marin County District Attorney’s Office decided against seeking the death penalty.

A preliminary hearing in the case was scheduled to begin next week.

Audrey Carey, who was visiting the Bay Area from Quebec, was found murdered in the park on Oct. 3rd. near where the Hardly Strictly Bluegrass Festival was being held.

Two days later, Steve Carter — a prominent Tantric teacher — was killed as he walked his dog on a trail in Marin’s Loma Alta Open Space Preserve and the trio allegedly stole his car to flee the Bay Area.

The trio was arrested in Portland outside of a soup kitchen on Oct. 7 and had Carter’s stolen car with them. They also had stolen property including Carey’s passport and the stolen gun allegedly used in the slayings.

Prosecutors say they believe Lampley was the gunman in both shootings.

The defendants are being prosecuted in Marin Superior Court for both homicide cases.