Two little girls, not yet old enough for kindergarten, were shot to death. Their infant sister was found asphyxiated.
All were discovered in a burning house with their 26-year-old mother, also a victim of a gunshot wound.
Police on Wednesday began releasing details of what they say was a murder-suicide at the Salem home on Tuesday.
Authorities said the children's father was found dead in a car 80 miles to the south. He is considered a person of interest in the slayings but his name was not released.
Firefighters who entered the burning home discovered the bodies of infant Sefi Lazukin, 1-year-old Zoe Lazukin, 3-year-old Angelica Lazukin and the children's mother, Natalya Lazukin.
They were an "absolutely wonderful family" with a close group of friends and strong relationships with extended family in Salem, said Peter Ignatovich, the Slavic Christian Church administrator who said he knew them well. They were at church most Sundays, he said.
He was skeptical the incident was a murder-suicide, noting that the police have not said conclusively that the father killed his family or himself.
"It was really disturbing to watch the news portray this monstrous kind of event," Ignatovich said. "I would not see him do it in any way. He loved his kids, loved his wife."
Authorities have not said if a weapon was discovered in the house they believe was intentionally set on fire.
Salem, the state capital, is about 50 miles south of Portland.
Clara King, who lives in an apartment about 50 yards from the home that burned, said she was awake in the middle of the night and heard a woman screaming, "like she was being hurt."
"I thought it was the neighbor lady having a party or something," King said. "I went out there to say something, but nobody was there."
Some residents of the working-class neighborhood say it is a rough area. It's not unusual to hear screams or fights in the middle of the night, King said.
The family was quiet and kept to themselves, said Jose Quiroz, who lives across the street. The father would frequently play with the children in the yard, where the kids splashed in a pool last summer, Quiroz said.
There were no outward signs of conflict between the couple, he said.
"It's unbelievable that someone could hurt their own kids," Quiroz said.
Another person found on a street a quarter mile north of the house was identified as 21-year-old Devin Matlock of Salem. He died of blunt force trauma, the result of two blows to the head, authorities said.
Matlock's death was being treated separately from the murder-suicide investigation, Salem police Lt. Dave Okada said.
Matlock was at a friend's house playing video games the night he died and left on foot about 2 a.m., said his friend Matt Wujcik.
Wujcik said Matlock usually avoided dark streets like the one where his body was found.
"It hasn't hit me all the way that I'm not going to see him," Wujcik said.
Matlock's sister said the family is in disbelief.
"Anybody who met him, they instantly liked him," said Amanda Matlock. "He's just going to be very, very missed."