A medical examiner found maggots in his clothing and skin in various stages of development that indicated he hadn't had a diaper change, bath or been removed from the seat in over a week.
When interviewed by deputies, Koehn said his girlfriend had fed the baby at 9am that day and everything seemed fine, and when she went to check on him between 11 and 11.30am, the baby was dead.
But the autopsy report relying on the findings of a forensic entomologist challenged the father's narrative.
The Iowa State Medical Examiner's Office ruled the death a homicide and determined the cause of death to have been failure to provide critical care.
The deceased infant was found weighing less than 3kg, placing him well below the 5th percentile in weight for a child his age.
Koehn's previous run-in with the law occurred in September 2016, when he was charged with second-degree theft for allegedly bypassing a water meter to his trailer home after his service was shut off for non-payment.
The charge was later dropped after Koehn agreed to pay restitution and fees.
Social media posts indicate that Koehn and Harris also have a 2-year-old daughter.
