Both cases involve murders in Surrey, B.C., the first in 2006 and the second in 2009.
David Mitchell, 25, was assaulted in October 2006 and sent to hospital with what were described as life-threatening injuries. He died two days later.
Police said they've now made four arrests in Mitchell's death.
Khalid Arnaout, 35, is charged with second-degree murder.
Three others have been charged with manslaughter and accessory after the fact: Charles Chambers, 32; Michael Yost, 34; and 32-year-old Kevin Pigott.
Mitchell's family issued a statement Monday in which they described him as a compassionate young man with a gift for writing, but also someone who struggled with drug addiction.
"Dave was taken from us with so much of his light left in him," the statement said.
"We had always believed that he would overcome his addiction and would have gone on to help others, a desire that he often expressed to those closest to him. Unfortunately, we will never know what could have been."
The second case involves the death of 25-year-old James Erickson, who was killed in early February of 2009.
Police officers responding to reports of gunfire in an apartment found Erickson dead.
David Sadler, 28, has been charged with first-degree murder, police said.
Erickson's mother, Patti, said in a written statement that her son's death has left the family in enduring pain.
"God gained an angel and we stay in grief with a very large piece of our hearts gone forever," the statement said.
The region's integrated homicide unit, which brings together the RCMP and several local police departments, launched a cold-case unit in 2012.
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