It couldn't be determined if the son of Heather Snively, in the last trimester of pregnancy, died before or after he was removed from the womb, the Washington County sheriff's department said in a statement.
A 27-year-old Beaverton woman, Korena Roberts, has been charged with murder in Snively's death. Police said she tried to claim the baby as her own. She appeared in court Monday but did not enter a plea.
A medical examiner said Monday that Snively had died of homicidal violence: "blunt force" and "sharp force" injuries.
"At this time, it has not been determined if she died because of head wounds she received or as a result of cutting injuries she received to her abdomen," the sheriff's office said.
A grand jury will hear the case, the prosecutor said, and Roberts might also face charges in the infant's death — if lab tests determine he ever took a breath.
"The issue is was the child alive at all at any point in time," said Washington Count District Attorney Bob Herman. "This is certainly unusual for its circumstances and nature."
Dr. Christopher Young, a deputy state medical examiner, said Snively and the infant appeared otherwise healthy. "There's no other reason she or the child would have died," he told The Associated Press.
Investigators said Mon-day that Roberts, who has two children younger than 10, had been telling friends and relatives for months that she was pregnant, and told many people she would have twins.
They said Roberts may have been in contact with other pregnant women in the Portland area. Herman said investigators assume that Roberts is not pregnant.
Snively had recently moved to Oregon from Maryland because her boyfriend and father of the child had found a job.
A 911 call on Friday brought emergency workers to Roberts' house in the Portland suburb Beaverton. Workers found blood on the floor and Roberts' boyfriend trying to revive the infant.
Investigators said Roberts claimed the baby was hers. At the emergency room, doctors, who were unable to revive the baby, determined that Roberts had not given birth.
Police came back to Roberts' home and found the body.
The boyfriend is cooperating and doesn't face charges, the sheriff's office said.
Family members say Snively and Roberts met through Craigslist, the on-line classified service, with Roberts soliciting baby clothes. Police said Monday they are still trying to confirm that.
Neighbors on Monday said Roberts reported being pregnant, bought a stroller at a garage sale and set up a crib on the front lawn of her rental home. They said Snively was seen at Roberts' house more than once.
Terry King, 61, said he had lived next door to Roberts for about two years. He said Roberts had told his wife, Bridget, about two weeks ago that she was pregnant and expecting soon.
"You get the impression that whoever did this must be crazy," King said. "But this woman didn't seem crazy on the surface."
Falisha Asmus said she and her mother-in-law, Wendy Pursinger, held a multiday garage sale, and about a week ago Roberts bought the blue stroller with teddy bears on the fabric.
Asked why she was buying a stroller, Roberts re-sponded that she was pregnant, Asmus said.
About three weeks ago, Asmus said, she saw Roberts setting up a crib in the front lawn.
The crib wasn't on the lawn on Monday. There was a blue plastic play pool, a broken yellow play tractor, offerings of flowers and a handwritten note, saying, "May God be with you."