Donovan Quinn Carter Cloud, 32, is being held in Northern Oregon Regional Corrections Facility in The Dalles, Ore., according to the jail's roster.
He's a suspect in the deaths of five people Saturday in the White Swan area.
Two additional suspects — Natasha Mae Jackson and Morris Bruce Jackson — are being held in the Yakama Nation jail, Casey Schilperoort, spokesman for the Yakima County Sheriff's Office, said Wednesday.
Dennis Overacker, 61, Michelle Starnes, 51, Thomas Hernandez, 36, Catherine Eneas, 49 and John Cagle, 59, were all shot to death in the 5100 block of Medicine Valley Road.
Donovan Cloud is being held in the Oregon jail because he was found by state police Sunday at Celilo Village, a small tribal community along the Columbia River about eight miles east of The Dalles, said Yakima County Sheriff Bob Udell.
James Cloud, a 35-year-old suspect arrested in Wapato early Monday, is being held at the Yakima County jail.
The Clouds were charged with assault with a dangerous weapon Monday in U.S. District Court.
Authorities have not said if charges are being pursued against the Jacksons.
Several police jurisdictions, the FBI, state patrol, Yakama Nation Tribal Police and the sheriff's officer are working on the case.
"It's important to note the general public is not endangered and should not be worried," Schilperoort said in an email. "The preliminary investigation appears the the homicides are drug-related. There is so much more investigating to be done to piece the story together."
EDITOR'S NOTE: This story has been updated with information about the Jacksons being held at the Yakama Nation jail.