CALDWELL, ID – Delbert Cornish was sentenced Wednesday to life in prison without the possibility of parole for the August 18, 2025 killing of his 18-year-old daughter, Onyx Cornish, and the attempted murder of her 15-year-old brother, Lucien Cornish.

Third District Judge Gabriel McCarthy imposed the sentence following a hearing in Canyon County court. Cornish was convicted of first-degree murder, attempted murder, and animal cruelty after prosecutors said he carried out a violent attack that also included the shooting of Onyx Cornish’s pet cat.

The Canyon County Prosecutor’s Office was represented by Chief Deputy Prosecutor Ingrid Batey and Deputy Prosecutor Stephanie Morse. Cornish was represented by defense attorney Erik Ellis.

In addressing the court, Batey described Cornish’s actions as “senseless, cruel, cowardly, and callous,” and asked the judge to sentence him to life without parole. “Delbert Cornish should wake up behind bars every day for the rest of his life,” Batey said. “That still isn’t enough, but it’s the closest this Court can get to true justice.”

Ellis requested a 25-year fixed sentence, citing Cornish’s struggles with depression and suicidal ideation. Judge McCarthy rejected that request and agreed with prosecutors, describing the crime as “an act of pure evil.”

In his final remarks from the bench, Judge McCarthy told the courtroom, “If there’s a God, perhaps God will have mercy on his soul. But the State of Idaho does not.”

Canyon County Prosecutor Chris Boyd thanked law enforcement agencies involved in the case, including the Caldwell Police Department, the Canyon County Sheriff’s Office, and the Canyon County Coroner’s Office.

“The Defendant’s actions were unthinkable and horrific, and he deserves to die in prison,” Boyd said. “I appreciate Judge McCarthy’s wise and thoughtful sentence, as well as his compassion for the victims in Court.”