Delbert Cornish, who was arrested for the murder of his 18-year-old non-biological daughter in August, has been sentenced to life in prison without the possibility of parole.

Cornish was charged with first-degree murder, attempted murder, and animal cruelty, according to a press release from the Canyon County’s Prosecuting Attorney’s Office. Cornish pleaded guilty to all charges in November.

He was sentenced by Third District Judge Gabriel McCarthy on Wednesday morning at the Canyon County courthouse for the murder of Hope “Onyx” Cornish, the attempted murder of her 15-year-old brother Lucian Cornish, and the killing of Onyx’s pet cat.

Police discovered a firearm and the 18-year-old’s dead body on Aug. 18, 2025 at a home on the 1600 block of Blaine Street in Caldwell. Delbert Cornish made a comment to his son about shooting another family member and was preventing his son from leaving the home, according to a press release from the Caldwell Police Department.

Eventually, the 15-year-old escaped and called 911, stating his father was inside the home with a gun. Delbert Cornish fled more than 60 miles from the scene to a residence in Mountain Home. The Caldwell Police Department said it used an automated license plate reader camera to detect his location.

KTVB reported that Cornish, who was 51 at the time of the killing, confessed to a Caldwell police detective that he had taken several shots of alcohol on the Monday morning of the murder before going into his daughter’s room and shooting her, stating to the detective he felt remorseful, according to a probable cause affidavit.

In the affidavit, Delbert Cornish told the detective he struggled with depression and had planned to take his and his children’s lives because he was tired of living with his brother who he claimed bullied them. Delbert Cornish believed the children “would not be able to carry on in life without him.”

Chief deputy prosecutor Ingrid Batey, who represented the prosecutor’s office along with deputy prosecutor Stephanie Morse, asked the court to impose a sentence of life in prison without the possibility of parole and described Cornish’s actions as “senseless, cruel, cowardly, and callous,” according to the press release.

“Delbert Cornish should wake up behind bars every day for the rest of his life,” Batey said. “This still isn’t enough, but it’s the closest this court can get to true justice.”

The press release stated that Cornish’s defense attorney, Erik Ellis, asked the court to impose a 25-year fixed sentence citing the defendant’s struggles with depression and suicidal ideation.

Judge McCarthy sided with the state and described the crime as “an act of pure evil” as he sentenced Cornish to life in prison without the possibility of parole. The press release stated that the judge gave final remarks to a packed courtroom.

“If there’s a God, perhaps God will have mercy on his soul,” McCarthy said. “But the State of Idaho does not.”

“The defendant’s actions were unthinkable and horrific, and he deserves to die in prison,” Canyon County Prosecutor Chris Boyd said in the press release.