A combination photo of Sean Angold, 24, Lila Alligood, 18, and Morrison Lampley, 23, are shown in these police booking photos provided by Multnomah County Sheriff's Office in Portland, Oregon, Oct. 9, 2015. Reuters

A young Northern California couple pleaded guilty Monday to murdering a Canadian backpacking tourist in San Francisco and a hiker in Marin County during a weekend in 2015. Morrison Lampley, 24, and his lover Lila Alligood, 19, pleaded guilty to the first-degree murders of Audrey Carey, 23, in Golden Gate Park and Steven Carter, 67, on a popular Fairfax hiking trail.

Lampley, who admitted to firing the weapon in both killings, will be sentenced to 100 years to life in prison. Alligood, who did not issue any shots, will get 50 years to life behind bars, according to local reports Monday.

Their co-defendant, Sean Michael Angold, 25, who previously pleaded guilty under a deal with the prosecutors, will be sentenced to 15 years to life in prison for second-degree murder. Angold agreed to testify against Lampley and Alligood at their preliminary hearing in September 2016 in exchange for a shorter prison sentence. Angold testified that the three drifters had used drugs he bought, including LSD, heroin and methamphetamine, throughout the weekend of the killings, according to local reports Monday.

Carey was in the middle of taking a solo-backpacking trip across the United States and Europe when she was robbed and then shot and killed in Golden Gate Park just north of San Francisco. Carey's body was discovered at the Hardly Strictly Bluegrass Festival on Oct. 3, 2015 with a bullet in her head, according to local reports Monday. Carter’s corpse was found two days later along a popular hiking trail near Fairfax, California, with multiple gunshots. His dog was also shot but survived.

Surveillance video at a gas station north of San Francisco showed the three suspects were driving Carter’s stolen car. And they were arrested in Oregon in October 2015 after law enforcement officers were able to track their location using the GPS from the car. Lampley and Alligood were found with the same handgun used in both killings, a .40 caliber pistol they had previously stolen from a truck.