Bail was set Friday at $25,000. The man, Robert Okerstrom, 26, is not allowed to have contact with his child or the child's mother.
A doctor said the baby's broken arm likely was the result of "a very forceful twisting motion," Snohomish County deputy prosecutor Andrew Alsdorf said in court Friday.
"We're dealing with a serious anger issue that is unpredictable and uncontrollable," he said.
Both the leg fractures apparently were "caused by twisting and turning commonly found in child abuse," according to a Marysville Police Department affidavit used to establish probable cause for the arrest.
Okerstrom's defense attorney Jon Scott asked for his release. Okerstrom has no criminal history and was going through a "period of frustration and rage" as a sleep-deprived new parent, Scott said.
The baby was taken to a doctor on Tuesday after his mother grew concerned. The woman sobbed throughout the hearing Friday. She also asked for Okerstrom's release.
Okerstrom was arrested Thursday and booked into the Snohomish County Jail.
Police were told that the boy's arm was broken in two places between the elbow and shoulder.
The boy's mother said she noticed trouble when Okerstrom handed off the baby to her between work shifts. Her son's arm was red, swollen and limp when she took him out of the car seat, she said.
When she touched his arm, the baby let out "a blood-curdling scream," she told a Marysville detective.
Okerstrom initially told her that nothing unusual had happened. He speculated to police that the broken arm could have occurred accidentally when he was trying to remove the child from his car seat.
He then offered another possible explanation, that he was afraid that he broke his son's arm when he squeezed him while trying to feed him a bottle.
Later, he allegedly admitted it occurred in a "fit of rage" while removing the boy from the car seat, the police report said.
He also allegedly said that "he was most likely responsible for the fractures in the legs," but he downplayed the cause saying he was playing with the child, court papers said.
An orthopedic doctor told police that the leg fractures are not consistent with normal play activities. He also found that it was "highly unlikely" that a 4-month-old would be mobile enough to cause them on his own.
Okerstrom also has been seeking counseling, the mother said.
Eric Stevick: 425-339-3446, firstname.lastname@example.org.
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