CARNATION, Wash. — Detectives painstakingly picked their way Thursday through the rural property where six people were killed Christmas Eve, and prosecutors prepared charges against the property owners’ daughter and her boyfriend, authorities said.

Hours after the bodies of the victims — reportedly three generations of the same family — were discovered, police arrested Michele Anderson, 29, and Joseph McEnroe, 29, according to a law enforcement official who spoke on condition of anonymity because he was not authorized to release the names.

King County Sheriff’s Sgt. John Urquhart would not confirm the suspects’ identities, but said they went to the crime scene after investigators had arrived, were questioned and arrested Wednesday. Investigators had not found a weapon, and the only hint of a motive they have disclosed is a long-standing dispute between Michele Anderson and her parents. Urquhart declined to elaborate on the nature of the dispute.

The owners of the property are Wayne Anderson, 60, and Judy Anderson, 61, according to public records. Multiple media reports said the couple, along with their son, Scott; his wife, Erica; and their two children, Olivia and Nathan, were the victims.

The sheriff’s office would only say the victims were the homeowners, ages 60 and 61, their daughter and son-in-law, both 32, and the younger couple’s 6-year-old daughter and 3-year-old son.

McEnroe and Michele Anderson were expected to make their first court appearance Thursday afternoon, and the King County prosecutor’s office planned to file charges against them Friday, Urquhart said. Authorities have not said what role either person played in the slayings, but Urquhart said both are expected to be charged with first-degree murder.

A message left Wednesday night at a telephone listing for a Michele Anderson in the Carnation area was not immediately returned.

The six were likely killed late afternoon or early evening on Christmas Eve, Urquhart said.

Authorities are trying to determine why deputies didn’t further investigate a 911 hang-up call on Christmas Eve that came from the house. The call ended after about 10 seconds, and the operator reported hearing “a lot of yelling in the background ... sounded more like party noise than angry heated arguing.”

Operators twice called back, but both calls went into voice mail. About 30 minutes later, two deputies arrived at the property, but found a locked gate and did not go onto the property. The dispatchers log reported the deputies saying, “gate is locked, unable to gain access.”