Two people have already pleaded guilty -- one to first-degree murder and the other to manslaughter -- in the deaths of Lisa Dudley and Guthrie McKay.
Dudley and McKay were shot in their home in Mission, B.C., in September 2008.
Justin Andrew MacKinnon is the latest to enter a guilty plea, admitting to two counts of manslaughter and receiving a sentence of seven years, minus time served.
Jack Douglas Woodruff pleaded guilty in March 2012 to two counts of first-degree murder, while Bruce Ian Main pleaded guilty in July of this year to two counts of manslaughter.
A fourth person, Tom Holden, was charged with two counts of first-degree murder and is currently awaiting trial.