ST. CLOUD – Jurors on Friday acquitted a Stearns County man accused of killing his newborn following a month-long trial with testimony from dozens of medical experts.

It's the second time 42-year-old Robert Kaiser went to trial for the 2014 death of his 2-month-old son William, whose doctors said he died of a traumatic brain injury presumably caused when the infant was alone in Kaiser's care.

The trial wrapped up Thursday afternoon and jurors returned verdicts of not guilty on two counts on Friday afternoon.

Baylea Kannmacher, an attorney with the Great North Innocence Project, argued the state's case was built on a "pile of maybes" that asked jurors to believe the bleeding in William's brain was a result of an assault. But the so-called assault left William with no scratches or bruises or a neck fracture, Kannmacher said.

According to court documents, Kaiser was caring for his son in Albany on Aug. 27, 2014, while the newborn's mother was at work. When she returned from work, William looked like a "ghost" — pale and limp, the prosecuting attorney said.

The baby was airlifted from the hospital in Albany to Children's Hospital in Minneapolis, where doctors worked to treat his seizures.

The doctors found bleeding in William's brain and eyes, as well as a bruise on his face and healing rib fractures, both of which can be concerning for a nonmobile infant.

Prosecuting attorneys asked the jury to find Kaiser guilty on two counts of murder, noting it wasn't necessary to prove intent, just that Kaiser caused William's acute head trauma.

"It can occur from shaking. It can occur from impact," Josh Kannegieter of the Stearns County Attorney's Office said during closing statements. "That afternoon, the defendant snapped and he hurt his son. What happened? Only two people were there. ... William cannot tell you what happened to him, but the medical evidence can."

At Children's Hospital, a medication intended to stop William's seizures made his blood pressure drop dangerously low, Kannmacher said, and a feeding tube perforated his bowel.

On Sept. 3, doctors found the boy's condition had deteriorated. They recommended he be removed from life support. An autopsy listed the death as a homicide.

Kannmacher told jurors that medical experts who looked at William's case after the fact reached a different conclusion than abusive head trauma. The infant had blood clots in his brain known as cerebral venous thrombosis (CVT), a condition that can cause many of the same symptoms attributed to abusive head trauma.

Kaiser's attorneys had experts testify that CVT can be very easy to miss. They also argued the doctors' presumptions of abuse at the hands of Kaiser blinded them to the real diagnosis.

What the evidence actually shows, Kannmacher said, was that William was a sick baby who had been vomiting for days and who appeared lethargic to the mother's coworkers the afternoon before he started having seizures.

"There's not just some reasonable doubt," Kannmacher said during closing statements. "There's more reasonable doubt than anything else."

After William's death over a decade ago, Kaiser was charged with three counts of murder. A Stearns County District Court jury in 2016 convicted him of two counts of second-degree unintentional murder and sentenced him to 20 years in prison. Kaiser was expected to serve about 11 years total in prison with the remainder on supervised release.

Then, in 2022, that same court vacated Kaiser's conviction after finding the state's experts gave false testimony that could have affected the trial's outcome.

During the first trial, an ophthalmologist had said the macular schisis found in William's eyes was caused by abusive head trauma. But he later clarified it "would be incorrect" to say that abusive head trauma is the only cause of the condition.

The Great North Innocence Project, which works to free people it believes are wrongfully convicted, started investigating Kaiser's case in 2020.

Last year, Stearns County decided to bring Kaiser to trial again. The local Innocence Project said it was its first retrial of a client.

"We are thrilled with the result," Kannmacher said Friday. "We have always believed in Robert's innocence. Now he can finally grieve the loss of his son and move on with his life."

Stearns County Attorney Janelle Kendall declined to comment on the verdict.

Sign up for the Minnesota Star Tribune's St. Cloud Today newsletter, with up-to-date news from central Minnesota each weekday.