The investigation began April 13 after 911 dispatchers received a call from a residence in the 700 block of Koontz Road about a baby not breathing, said Lewis County Chief Deputy Stacy Brown.
The baby girl was transported to Centralia Providence Hospital initially but due to the severity of injuries was transferred to Mary Bridge Children's Hospital in Tacoma.
Doctors reported the infant had suffered retinal hemorrhaging and a brain injury consistent with shaken baby syndrome.
Investigators then learned that the baby girl's father, Tyler C. Abair, was alone with her prior to her injuries.
When questioned by detectives he denied injuring or shaking the baby. But as the investigation progressed he eventually admitted to shaking the child but stated he only did so after the baby began choking while drinking a bottle, Brown said.
Abair said he then noticed the baby had stopped breathing after he shook her but did not call 911. He instead called the baby's mother at work nearby, according to investigators. The mother had someone call 911 immediately, rushed home and began CPR.
In their examination of the baby, doctors found old injuries to the infant's brain which also appeared to be from being shaken.
This week, detectives received medical reports to confirm their suspicions of abuse, Brown said.
Abair was booked into the Lewis County Jail Tuesday for investigation of first-degree assault of a child.
The baby is now recovering at home with her mother.