"It was clearly and intentionally barricaded," said Sgt. Cindi West with the King County Sheriff's Office.
Fire crews arriving Sunday morning also found at least five gas cans in the house outside Seattle that appeared to be full of gasoline, West said.
Detectives with the major crimes unit were assigned to the case. The King County Medical Examiner's Office removed the bodies Sunday, and autopsies will determine how the women died.
No one else was found in the home near North Bend. A couple and their daughter live in the house, but the identities of the victims have not been confirmed and police have not identified suspects, West said.
"We're not calling anybody a suspect because we don't know what we have," she added.
A bomb disposal unit called in to clear the house found a suspicious device, but investigators later determined it was not an explosive, West said.
Cate Reynolds walked to the scene Sunday afternoon with her daughter and other friends, who said they were best friends with and recently graduated from the same high school as a young woman who lived in the house. "They wanted to just come and be close and process some stuff," Reynolds said.
Investigators searched for a 2003 blue-grey Toyota Corolla missing from the home, and found it unoccupied in North Bend on Sunday afternoon.
"We don't know that there is a suspect associated with the vehicle, we just want to know where the vehicle is," West said earlier Sunday before the vehicle was found.
A neighbor reported the house fire Sunday morning in this rural, wooded community in the foothills of the Cascades, about 30 miles east of Seattle. Firefighters found the women's bodies and pulled them outside. Attempts to resuscitate them were not successful.
Firefighters were unable to go back into the house because of the gas cans and other safety reasons. Crews were able to put the fire out about an hour later.