by Audrey Dutton, photography by Natalie Behring for ProPublica

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A police officer heard wailing as he approached the house in a farming community near Idaho Falls, Idaho. It was freezing cold in the predawn darkness of 6:10 a.m. on Feb. 1, and Alexis Cooley was “hysterical,” the officer wrote later. He followed her into the house.

To Alexis, nothing felt real in that moment. It was like her eyes were a video screen playing a movie. More officers and sheriff’s deputies arrived. An ambulance pulled up. When Alexis called 911 minutes before, she’d said between sobs and frantic pleas for help that the baby wasn’t breathing and his body was cold. Medics performed CPR on her newborn son’s 12-pound body, though it was futile.

Still, the medics asked: Would you like us to take him to the hospital? Yes, save my baby, Alexis remembers saying, and soon she was in her husband Diamond’s pickup truck, following the ambulance to the hospital.

The doctor pronounced Onyxx Cooley dead two minutes after arrival.

In the hours that followed, as Alexis and Diamond Cooley sat with their baby’s body, the search for answers about what took his life was supposed to begin. The person whose job is to find those answers, the elected coroner of Bonneville County, failed to do so.

He never asked Alexis and Diamond about the days preceding Onyxx’s death, never visited the scene, never performed a reenactment of the infant’s sleeping position, never ordered an autopsy. Some or all of these steps are prescribed by the Centers for Disease Control and Prevention, the U.S. Department of Justice, the National Association of Medical Examiners and the American Academy of Pediatrics when an otherwise healthy infant dies.

The guidelines exist to help coroners identify accidental suffocation, abuse or medical disorders that went undetected. The guidelines also make it possible to flag risks that, if discovered, may help keep other children alive.

“If you don’t look, you’re not going to find,” said Lauri McGivern, medicolegal death investigator coordinator in Vermont’s Office of the Chief Medical Examiner, chair of the National Association of Medical Examiners’ medicolegal death investigation committee and past president of the American Board of Medicolegal Death Investigators. “We need to know why infants are dying.”

But nothing in Idaho law says an elected county coroner must follow any national standards for death investigations. So, many of them don’t.

A child who dies unexpectedly or outside of a doctor’s care in Idaho is less likely to be autopsied than anywhere else in the United States.

In the case of baby Onyxx, without a word to Alexis or Diamond, Bonneville County coroner Rick Taylor simply decided the death was an unsolvable mystery.

Alexis Johnson and Diamond Cooley met on Tinder shortly after high school and became parents to Jasper in 2019, Stohne in 2021 and Onyxx in 2023.

The Cooleys got married after Jasper was born. They separated a few years later, while Alexis was pregnant with Onyxx. The breakup wasn’t painless, but they worked through it. These days, they still speak in the shorthand of old friends and try to comfort each other; when Alexis starts to cry while talking about Onyxx, Diamond cracks a joke at his own expense, and she laughs.

They agreed to share custody of the boys. Diamond moved in with his mother in Idaho Falls, while Alexis stayed at her parents’ house in Shelley, about 20 minutes away.

Based on prenatal ultrasounds, they weren’t surprised when Onyxx was born with a cleft palate and lip. It required road trips to see specialists in Salt Lake City and made feeding a little more complicated. Onyxx couldn’t breastfeed. He needed a special bottle. After a couple of scares — Onyxx choked on spit-up when she put him on his back — Alexis talked with his doctors and learned she should keep his upper body elevated for 30 minutes after he ate, to leave time for him to digest the formula.

But otherwise, Alexis couldn’t believe what an easy baby he was. He almost never cried — just smiled, cooed and kept his eyes on his big brothers. Alexis loved to watch Jasper or Stohne get up close to Onyxx, hold his hands and play with him; he would burst into kicks and smiles. Diamond remembers that as soon as Onyxx figured out how to smile, he never seemed to stop.

What happened during the baby’s final hours is captured in police reports, 911 dispatch logs, a 911 call recording, Onyxx’s hospital records and Alexis’ recollections.

The night of Jan. 31, after putting their two older sons to bed, Alexis sat in the living room feeding Onyxx until he dozed off around 11 p.m. She carried him downstairs to their basement bedroom, where he lay propped on her legs facing her, while she sat playing Fortnite in bed.

As she lay down to sleep, Alexis propped a swaddled Onyxx in the crook of her outstretched arm. She woke expecting to feed him again around 3 a.m., but for the first time in his 10 weeks of life, Onyxx wasn’t ready for another meal. He was sound asleep, so she moved him off her arm and onto his back. She scooted over to the other side of the king-size bed, checked her phone, took a puff from an e-cigarette on her nightstand, then went back to sleep.

When she woke again around 6 a.m., Alexis rolled over to find Onyxx in the same position, swaddled. He was cold. A half-inch of yellowish-white foam came from his mouth. It looked like saliva with a little bit of blood in it.

Alexis tried to clear his airway — first with her finger, then by turning him over and doing the Heimlich maneuver she learned in a health care course. She ran upstairs with Onyxx, screaming for help. She called 911 and got some words out before handing the phone to her mother. Then Alexis called Diamond, who jumped in his truck and got to the house as the ambulance doors closed.

With Alexis and Diamond following behind in the pickup, the ambulance carrying Onyxx arrived at the emergency room of Eastern Idaho Regional Medical Center at 6:43 a.m. An ER doctor looked at the baby’s heart through an ultrasound. There was no life. Onyxx’s parents walked through the ER doors and, minutes later, the doctor delivered the........

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