When Zachary Paul Koehn called an ambulance to his Iowa home just before 1 p.m. on Aug. 30, he told the dispatcher that his girlfriend, Cheyanne Renae Harris, had fed their 4-month-old baby just hours before and had last checked on him at 11 a.m. When Harris went to check on him again a half-hour later, their baby was dead, Koehn said, according to court documents.

But the State Medical Examiner ruled the death a homicide, with the cause of death "a failure to provide critical care."

An autopsy suggests deputies from the Chickasaw County Sheriff's Office came upon a grim scene: the baby, weighing less than seven pounds, had maggots "in various stages of development" in his clothing and on his skin. For more than a week, Sterling Daniel Koehn had not had a diaper change or bath, or been taken out of a powered baby swing inside one of the home's bedrooms, according to the complaint affidavit.

"The facts of this case go far beyond neglect and show circumstances manifesting an extreme indifference to human life," the court documents said.

On Wednesday, Koehn, 28, and Harris, 20, were arrested and charged with child endangerment causing death, a class B felony, and first-degree murder, a class A felony punishable by life in prison. The couple lives in Alta Vista, Iowa, a town of fewer than 300 people about 170 miles northeast of Des Moines. According to the complaint affidavit, the couple has another child.

Koehn initially told police that Sterling died after his 911 call. But he and Harris later claimed the baby had not been checked on since the previous day. Their stories are inconsistent with the findings of the autopsy, authorities say.

Dennis Klein, the chief state medical examiner in the Iowa State Medical Examiner's Office, said that all cases involving babies - especially homicides - are "pretty horrific and difficult to deal with." He described the details of Sterling's death included in the complaint affidavit as "pretty explicit."

Severely underweight and only 14 inches long, Sterling was well below the 5th percentile in size and weight.

It was not immediately clear where Koehn and Harris were arrested. After arrest warrants were issued on Wednesday, the Chickasaw County Sheriff's Office was helped by the Charles City Police Department, Fayette County Sheriff's Office and Mitchell County Sheriff's Office in finding the couple. The Iowa Division of Criminal Investigation is also involved in the case.

Koehn and Harris are being held on $100,000 cash-only bond, according to the Chickasaw County Sheriff's Office. A preliminary hearing is set for Nov. 2. It wasn't immediately clear whether Koehn and Harris had attorneys. They could not be immediately reached for comment.