SEATTLE — King County sheriff's investigators have arrested two suspects in connection with the slayings of six people in a rural Carnation home Wednesday morning.

The man and the woman haven't been identified, but are described as being in their late 20s or early 30s. Charges are expected to be filed at the end of the week, said sheriff's spokesman John Urquhart.

"I'm not sure what the relationship is between the victims and the suspects," Urquhart said. "We now have to process the scene."

Detectives are investigating the deaths as homicides near this town about 21 miles from Seattle. Murder-suicide in the Christmas Eve deaths has been ruled out, the King County Sheriff's Office said.

Among the victims were a woman and man in their 50s, a woman and man in their 30s, and a girl, 6 and a boy, 3, said Sgt. John Urquhart. He did not explain the relationships among the people.

Around 8 a.m. Wednesday, a co-worker of one of the victims went to the home. The co-worker said the person had not shown up for work and had always been very reliable.

The co-worker discovered the victims and called 911, said Detective Bob Conner.

A local postal carrier and a Boeing engineer live at the home, according to people who knew them. The couple have three adult children — at least one of whom lives on the property, said a family friend.

Officials did not confirm if they were among the victims.

"We have an investigation of suspicious deaths," said Conner. He said there were "no threats to any neighbors in the area" but wouldn't elaborate on why he believes that.

A family friend Mark Bennett, 58, had called one of the family members on Christmas Eve, and said everything seemed fine. The person told him the family would be getting together for Christmas, but when he called on Christmas Day, his call went to voice mail.

Conner called it a "complex and large" investigation involving the King County Sheriff's Office major crimes unit.

About 15 to 20 people are at the scene gathering evidence. They're still searching the woods at the rear of the property for additional victims. They are searching for a suspect or suspects.

The Medical Examiner will release the cause and manner of the deaths.

The deaths mark the state's worst mass slaying since Kyle Huff, 28, killed six people and wounded two others in a Capitol Hill house before fatally shooting himself on March 25, 2006.

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(Siderius and Seattle Times reporter Jennifer Sullivan compiled this report.)