A Caldwell man accused of killing his teenage daughter is being held in Canyon County custody without bail after a shocking confession detailed in newly released court records. Delbert Cornish, 42, was arrested Monday evening in Mountain Home before being transferred to Canyon County on Tuesday.
He appeared in court on Wednesday, where he was appointed a public defender. Court documents obtained by Idaho News 6 through a public records request revealed Cornish admitted to the crime, telling detectives, “I’m not gonna lie, I did it, dude.”
The Canyon County Coroner identified the victim as 18-year-old Hope Cornish, known to loved ones as “Onyx.” Family members said Delbert had adopted her years ago. According to a probable cause affidavit, Cornish told investigators he had long struggled with alcoholism and depression.
He claimed he had been planning to kill all three of his children and then himself since buying a gun last fall. He said the plan unraveled when his oldest son was returned to prison for a parole violation. Cornish explained he lost his job two weeks ago and kept it secret from his brother, with whom he shared the Caldwell home just blocks from the county jail.
On Monday morning, Cornish reportedly told his brother, “Today was the day,” without explaining what he meant. He later described to officers how he lingered outside Onyx’s bedroom, debating his next move. When she opened the door, he shot her in the head, local NBC affiliate KTVB reported.
He told detectives he then stood over her for 20 minutes as she “gasped for breath.” Overcome with emotion, Cornish told officers, “I’m a piece of s***, man. I’m not going to lie, I did it.” A GoFundMe posted for “Onyx” Cornish begins with a firm accusation: “Onyx was killed [by] her father.”
Afterward, court records say he covered Onyx’s body with a Pride flag “as a way to honor her,” killed her cat, and flew into a rage, punching holes in walls and swinging a hatchet at her bedroom door. He later wrote a confession and suicide note, drank bourbon, and watched television until his younger son came home.
When his son arrived, Cornish admitted to killing Onyx and tried to force him to see the body. At one point, Cornish fired a shot into the floor and pointed the weapon at his son. The teenager managed to disarm him and escape to call 911.
Cornish then fled to his ex-girlfriend’s home in Mountain Home, where he was arrested Monday night. Onyx’s aunt, Debbie Duran, said the family is devastated and is raising money to cover funeral costs. Cornish is scheduled for a preliminary hearing on September 3.