Three young sisters who were found dead near a Washington campground after they left home for a “planned visitation” with their father died from suffocation, authorities said Monday.

Paityn Decker, 9; Evelyn Decker, 8; and Olivia Decker, 5, were located on June 2 near the Rock Island Campground in Chelan County, Washington, following a search, police said.

An autopsy completed on Friday determined the girls’ cause of death to be suffocation and the manner of death is homicide, according to the Chelan County Sheriff’s Office.

Three young sisters, Paityn Decker, 9, Evelyn Decker, 8 and Olivia Decker, 5 have been missing since May 31 after leaving for a “planned visitation” with their father, according to the Wenatchee Police Department.