SAN FRANCISCO -- Prosecutors on Tuesday identified the alleged triggerman among the three transients charged with the shooting deaths of a Canadian backpacker and a yoga instructor in Northern California last week.

A criminal complaint filed Tuesday in Marin County Superior Court charges Morrison Haze Lampley, 23, with pulling the trigger of a stolen Smith & Wesson handgun in both killings while the trio robbed their alleged victims.

Lampley and his two travelling companions are all charged with multiple murders with special circumstances that include lying in wait for their victims, making them eligible for the death penalty. Lampley, Sean Michael Angold, 24, and Lila Scott Alligood, 18, are scheduled to make their first court appearances Wednesday. They have not been appointed lawyers.

The three are charged with killing Canadian backpacker Audrey Carey, 23, whose body was found shot in the head in Golden Gate Park on Oct. 3. Carey had just embarked on a backpacking trip and had camped in Golden Gate Park during the popular Hardly Strictly Bluegrass music festival in the park.

The trio is also charged with killing tantric yoga instructor Steve Carter, 67, on Oct. 5.

Carter's body and his wounded dog were found near a popular hiking trail in Marin County, about 20 miles (32 kilometres) north of San Francisco. San Francisco Police commander Toney Chaplin said both victims and Carter's dog were shot with the same handgun, which was reported stolen om Oct. 1 from an unlocked car in San Francisco Fisherman's Wharf neighbourhood. Carter's dog is expected to survive. All three are also charged with animal cruelty, though the criminal complaint alleged that Lampley pulled the trigger.

Marin County Sheriff's Lt. Doug Pittman said the three suspects have "no fixed address." They were arrested outside a Portland, Oregon soup kitchen on Wednesday. Investigators and the criminal complaint say they were found in possession of the stolen gun, Carter's Volkswagen station wagon and Carey's tent, sleeping bag, day pack and other possessions, including her passport and airline tickets.

The Marin County District Attorney Edward Berberian said a decision on whether to pursue the death penalty will be made later. He said the office will conduct a "detailed review process" before deciding whether to ask a jury and judge to sentence a murder defendant to death. California hasn't executed anyone since 2005.

The criminal complaint further charges the triggerman with being a felon in possession of a gun. The criminal complaint states that Lampley was convicted in July of receiving a stolen car in San Diego.