Chelsea Yellowbird from the Samson Cree First Nation was shot and killed at her home on Sept. 5, 2011.
RCMP last week arrested two men and charged them with first-degree murder.
A warrant was issued for a third suspect and Mounties say he was taken into custody on Friday.
Twenty-year-old Wacey Applegarth of Hobbema is also charged with first-degree murder.
Yellowbird was killed outside her home two months after her five-year-old nephew, Ethan Yellowbird, was killed by a gunshot while sleeping in his bed next door.
Also charged are Randall Omeasoo, 21, and Shelby Minde, 23, both of Hobbema.
The reserve, about 90 kilometres south of Edmonton, has struggled with drug- and gang-related violence over the years.
Three teens pleaded guilty to manslaughter last year in youth court in Ethan Yellowbird's death. They admitted to taking turns firing a gun at a home, accidentally killing the boy.
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