An Idaho father is set to admit guilt in the tragic killing of his adopted daughter, as his attorney announced during a Tuesday court session in Canyon County. The case involves Delbert Cornish, 51, who faces charges of first-degree murder following the death of 18-year-old Hope “Onyx” Cornish this past August. Initially, Cornish was charged with aggravated assault, but this was later escalated to assault with intent to commit murder, alongside an additional charge of animal cruelty, according to reports from Law&Crime.

Whether Delbert Cornish has negotiated a plea agreement regarding the murder charge remains uncertain.

“When I saw him in court, it was as if my blood turned to ice,” expressed Hope Cornish’s mother, Crystal Thompson, in her recount to the media outlet. “I started trembling, overcome with a deep sense of despair.”

On Tuesday, the defendant returned to court, this time with a shaved head. As Delbert Cornish sat, his lawyer rose, telling the presiding judge that “at this time, Mr. Cornish would like to change his plea to guilty,” per courtroom video shot by Boise-based ABC affiliate KIVI.

Thompson, who reportedly had a long-term relationship with Delbert Cornish, recounted, “He glanced my way, quickly turned his gaze, and avoided eye contact after that. He must confront the reality of his actions, and the situation is far from just.”

The tragic incident unfolded on August 18, described by authorities as a “horrific act of family violence.” On that morning, around 9 a.m., at a residence on the 1600 block of Blaine Street in Caldwell, a suburb near Boise, court records indicate that Delbert Cornish consumed several shots of alcohol before entering his daughter’s room and fatally shooting her in the head.

On Aug. 18, a “horrific act of family violence” occurred, as authorities would later recount. At a home on the 1600 block of Blaine Street in Caldwell, a suburb of Boise, Delbert Cornish took several shots of alcohol around 9 a.m., according to court documents obtained by local outlets. He then entered his daughter’s bedroom and reportedly shot her in the side of the head.

The defendant then kissed her on the cheek and shot her cat “for the same reasons, because no one would take care of it after they were all dead,” a probable cause affidavit says. Delbert Cornish is said to have then covered Hope Cornish’s body with a large pride flag “as a way to honor her, because it was something that meant a lot to her.”

Background: The 1600 block of Blaine Street in Caldwell, Idaho (Google Maps). Inset: Delbert Cornish (Canyon County Sheriff’s Office).

He had been planning to kill his daughter, two sons, and himself for nearly a year, ever since he bought a black 9 mm Hi-Point handgun in September or October 2024, law enforcement said. And on that August day, as the hours passed after the shooting, Delbert Cornish allegedly waited for his youngest son Lucian Cornish — who is reported to have been either 14 or 15 years old — to come home from school.

When the teen arrived, Delbert Cornish reportedly asked him how school was before telling him “he had killed his sister.” The defendant also tried to convince the boy to “check on his sister,” but the son refused, the affidavit states.

“Delbert then went to the couch [and] grabbed a gun,” at which point his son said he wanted to leave, the court document adds. But the defendant did not intend to let that happen, authorities maintain. He allegedly “shot at the ground,” blocked the doorway, and pointed the gun at his son’s chest.

They fought over the gun, according to Lucian Cornish, with the son eventually winning control over it and running away to call 911.

When law enforcement officials arrived at the home after 4 p.m., they found the magazine, the handgun, and a “large note written on the wall” that appeared to be a possible murder-suicide note. It reportedly included statements such as “I’m a man of my word my kids died by my hand. I’m tired of them being made fun of,” and “I’m going! My kids are going with me.”

Police found Hope Cornish and her cat dead. The defendant was arrested about 70 miles southeast heading to his ex-girlfriend’s home, local NBC affiliate KTVB reported.

Delbert Cornish confessed to killing his daughter and “began to cry” when an officer said they had found his daughter’s body, according to the affidavit. “I’m not gonna lie, I did it dude,” the defendant allegedly said, unprompted.

The court document also suggests a possible motive for the defendant’s alleged crimes.

“Delbert admitted to me that he is an alcoholic who struggles with depression,” it states. “Delbert explained he wanted to kill his children along with himself because he believed nobody … would take care of them once he was dead, and that they would not be able to carry on in life without him.”

A change of plea hearing is reportedly scheduled for Nov. 12. Lucian Cornish has been by his mother’s side as they seek “justice” for Hope Cornish’s killing, and as the mother told KIVI, they plan to be there when Delbert Cornish learns his fate.