The Canyon County case also included an attempted murder count involving the victim’s 15-year-old brother.
CALDWELL, Idaho — A Canyon County judge on Jan. 28 sentenced Delbert Cornish to life in prison without the possibility of parole for the Aug. 18, 2025 killing of his 18-year-old daughter, Hope “Onyx” Cornish, and the attempted murder of her 15-year-old brother in Caldwell.
The sentence caps a wrenching case that drew standing-room crowds to the Third District courtroom and strong words from the bench. Judge Gabriel McCarthy called the crime “an act of pure evil” and sided with prosecutors who sought life without parole. The ruling followed arguments from both sides and formal statements recognizing police and county investigators who handled the case. The decision means Cornish will spend the rest of his life in state custody, while the surviving teen continues to recover from the violence that unfolded inside the family’s home.
According to the court record summarized in open court, police were dispatched to the family’s Caldwell residence on Aug. 18, 2025. Responding officers found Onyx Cornish dead from a gunshot wound and evidence that her younger brother had also been targeted. Prosecutors said Cornish’s actions extended to animal cruelty, noting that the teen’s pet cat was shot. Chief Deputy Prosecutor Ingrid Batey told the court the attack was “senseless, cruel, cowardly, and callous.” Judge McCarthy, addressing a packed gallery, said, “If there’s a God, perhaps God will have mercy on his soul. But the State of Idaho does not.” Defense attorney Erik Ellis asked for a 25-year fixed term, citing the defendant’s depression and suicidal thoughts, but the judge rejected that request.
Officials identified the victims as Hope “Onyx” Cornish, 18, and her brother, 15. The Canyon County Prosecutor’s Office said Batey and Deputy Prosecutor Stephanie Morse handled the case. Investigative support came from the Caldwell Police Department, the Canyon County Sheriff’s Office and the Canyon County Coroner’s Office. The court noted the date of the killing as Aug. 18, 2025, in Caldwell. Prosecutors argued that the brutality of the crime, the attempted killing of a second child and the additional cruelty charge warranted the maximum sentence. The defense did not dispute the loss of life but asked the court to factor in mental health issues; the judge said those arguments did not outweigh the facts of the case. Whether additional evaluations will occur in prison remains unknown.
Public records show the case advanced through Idaho’s Third Judicial District in the months after the killing. Sentencing occurred Wednesday, Jan. 28, before Judge McCarthy. No capital charges were at issue; prosecutors pursued a life term without parole on the murder count, along with time for attempted murder and animal cruelty. The court’s oral pronouncement set life without parole on the murder count and additional consecutive time on the remaining counts. The clerk recorded the judgment the same day. The defendant was remanded to state custody following the hearing.
Community members filled the courtroom, some wearing clothing in Onyx’s favorite colors. A relative quietly described the teenager as creative and kind. “We want people to remember her for her life, not for her death,” the teen’s mother said after the hearing. Prosecutor Chris Boyd thanked local police and deputies for their work and said the sentence ensures public safety. Outside the courthouse, a neighbor said the case “shook” the area, adding that people were relieved to see the verdict and sentencing phase end.
The judgment stands as of Friday, with Cornish in state custody and no parole eligibility under the life sentence. Any notice of appeal would be due under Idaho’s normal timelines, and the court docket will show the next administrative step.
Author note: Last updated February 1, 2026.