Police: Couple arrested in slayings of six on Christmas Eve
The pair, who are in their late 20s, were being taken to the King County Sheriff's Office on Wednesday evening, deputies told CNN.
The bodies were found earlier in the day at a house in Carnation, about 20 miles east of Seattle.
The pair have not confessed to the deaths and do not yet have access to lawyers, King County Sheriff's Sgt. John Urquhart said Wednesday evening.
"This couple was among the people that showed up at the [crime] scene," Urquhart said. "And as we got to talking to them, we developed probable cause and made the arrests."
The couple is expected to be charged with six counts of first-degree homicide, he said.
Urquhart said investigators have not yet determined a motive for the killings. He said the two suspects are girlfriend and boyfriend and are related to the victims.
A law enforcement official who spoke on condition of anonymity told The Associated Press that police arrested the property owners' daughter and her boyfriend.
The victims were a man and a woman in their 50s, another man and woman in their 30s, and two children: a 6-year-old girl and a 3-year-old boy.
They are believed to be three generations of the same family, and they appeared to have been shot sometime Monday, Urquhart said.
The bodies were found in and around the house, which is on a residential property in Carnation, Urquhart said. The house sits among a cluster of residences and is at the end of a long dirt road on the edge of woods.
A colleague of one of the victims came by to check on the family Wednesday morning after one of the victims didn't show up for work, King County Sheriff's Sgt. Jim Laing said.
The colleague called deputies, who initially found the bodies of two adults and a child inside a house on the property.
A subsequent search revealed the other bodies.Authorities earlier ruled out murder-suicide in the deaths.