Idaho Father Charged with Murdering Daughter and Attacking Son in Caldwell Home

Onyx Cornish was killed Aug. 18, 2025 in Caldwell, Idaho

Delbert Cornish, 51, has been charged with first-degree murder and aggravated assault after allegedly killing his 18-year-old daughter, Onyx Cornish, and attacking his younger son in a Caldwell, Idaho home, authorities report. Cornish is being held without bond at the Canyon County Jail.

Court documents indicate Cornish had been planning the killings for nearly a year, purchasing a black 9mm Hi-Point handgun in late 2024. On Monday morning, Cornish reportedly consumed several shots of alcohol before entering his daughter’s bedroom and shooting her in the side of the head. He then allegedly killed the family cat, citing concern that no one would care for it after the family’s deaths. Cornish reportedly covered his daughter’s body with a large gay pride flag to honor her.

Onyx Cornish, left, with her mother, Crystal Thompson. Onyx, 18, was killed on Monday. Her father, Delbert Cornish, has been accused of killing her and charged with first-degree murder

Hours later, when his younger son arrived home, Cornish allegedly attempted to force him to check on his sister and blocked the doorway with a gun. The teen wrestled the firearm away and fled to call 911. Police arrived around 4 p.m., discovering a handgun and magazine in the living room, as well as a large note on the wall, believed to be a murder-suicide message, stating, “I’m a man of my word my kids died by my hand… I’m going! My kids are going with me.” Hope Cornish was found dead in her bedroom with a hatchet embedded in the exterior of the door.

Cornish was located in Mountain Home while heading to his ex-girlfriend’s home and was arrested without incident. He allegedly admitted to the killing, expressing remorse and indicating he had not shot his younger son out of love. According to the affidavit, Cornish cited alcoholism, depression, and frustration over his children being bullied as motives. He reportedly intended to kill all three children but was prevented from targeting an older son due to the child’s prior incarceration. Cornish admitted attempting to take his own life but found the gun would not fire.

The 1600 block of Blaine Street in Caldwell, Idaho. Inset: Delbert Cornish

Caldwell Chief of Police Rex Ingram condemned the act as a “horrific act of family violence” and praised the coordinated law enforcement response in apprehending the suspect. Cornish’s preliminary hearing is scheduled for September 3.