MOUNT PLEASANT, Ia. — Sterling Koehn was left in his baby swing in a hot, stuffy room for at least nine days before his father decided to call 911, prosecutors said Tuesday.

The infant, not yet four months old, died last year of malnutrition, dehydration and infection. His weight at the time of his death was not much more than his birth weight — just under seven pounds.

Sterling's parents, 29-year-old Zachary Koehn and 21-year-old Cheyanne Harris, are charged with first-degree murder and child endangerment causing death. They have pleaded not guilty. Testimony in Koehn's trial began Tuesday in Mount Pleasant.

During the week and a half or more that Sterling was left in his swing, Koehn and Harris continued to clothe and feed their 2-year-old daughter, said Assistant Iowa Attorney General Coleman McAllister. The girl was in good health when law enforcement arrived at the family's Alta Vista apartment on Aug. 30, 2017.

"This is not a case, the evidence will show, where you hear about a young inexperienced parent or somebody who did not know how to care for children," McAllister said.

Nor is it a case of the parents not having adequate resources to care for their children, he said. Koehn made $45,000 a year and had access to health insurance as a truck driver for Nugent Nuggets, hauling chickens from Wisconsin to Charles City, Iowa.

Koehn's attorney, Les Blair, said Sterling's death was "a tragedy, not a crime."

Blair urged the jury to avoid a rush to judgment in Koehn's case and asked them, once they've heard all the evidence, to return a not guilty verdict.

"You need to make sure that you keep an open mind, that you listen to all the evidence and that you don’t draw any conclusions or reach any conclusions until after you’ve heard everything," Blair said.

In opening statements Tuesday morning at the Henry County Courthouse, prosecutors described the last days of Sterling's life in graphic detail.

"The feces that sat in that diaper ate through his skin, allowing E. coli bacteria that was in his diaper and in his stool to enter his bloodstream and cause an infection," McAllister said.

The hot room attracted flies, which laid eggs that hatched into maggots while Sterling was alive, McAllister said. Those maggots crawled in his clothes and his diaper for days.

Koehn called 911 on Aug. 30, 2017 and told the dispatcher that Sterling had died of sudden infant death syndrome, McAllister said. But that wasn't true.

"This was not an accident. That was a cover story concocted by this defendant to cover the awful truth," he said.

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A forensic entomologist examined the insects on Sterling's body and concluded the baby had been in his swing for at least nine and as many as 14 days, wearing the same diaper the whole time, McAllister said.

When Koehn was interviewed by law enforcement, McAllister said he told the officer he had played with Sterling within the last day.

"He said that Sterling was a healthy baby," McAllister said. "There was nothing wrong with him. That when he played with him he appeared to be alert and happy."

"It would have been obvious to anybody that Sterling was not right," McAllister said.

"He was not a normal, healthy child."

When Koehn first spoke with law enforcement, he denied anyone in the home was using drugs. But in a follow up interview several days later, McAllister said Koehn admitted to providing drugs to Harris and to using methamphetamine twice a week.

Court records show Harris may use intoxication as a defense at her trial, which has not been scheduled. Harris reported last using meth two to three weeks before her son's death.

McAllister said a friend of Koehn's who occasionally came over to use drugs together will testify at his trial that the door to Sterling's bedroom was always closed.

"He did not even know that they had a baby," he said.