A 23-year-old woman has been arrested.
The baby boy, nearly full-term, was hospitalized at Deaconess Medical Center in Spokane in critical condition.
Court documents said 27-year-old Araceli Camacho Gomez, of Pasco, had her hands and feet bound with yarn and suffered "massive trauma to her stomach area" late Friday night. An autopsy showed she died of the chest wounds, but had other wounds "consistent with the cutting of the body to remove an unborn child."
Her body was found early Saturday in Kennewick's Columbia Park.
A Kennewick woman, Phiengchai Sisouvanh Synhavong, has been arrested for investigation of first-degree murder and is accused of trying to pass the infant boy off as her own in calls made late Friday night to emergency dispatchers. She was being held without bail Monday, with another court appearance scheduled Wednesday.
Court documents say gloves soaked in blood, a boxcutter, bloody paper towels, yarn, baby bottle and baby socks were among some of the items found in Sisouvanh Synhavong's purse.