Denton murder defendant found not guilty by insanity defense
By Brooke Colombo, Staff Writer – Denton Record Chronicle, Aug 26, 2026 – Original Article
A Denton murder defendant was recently found not guilty of his mother’s murder by reason of insanity after he spent over seven years in custody.
Isaac Israel Warriner, 30, was arrested in May 2019 on suspicion of killing and decapitating his mother at their shared apartment in the 2400 block of Stockbridge Road.
A psychologist determined in 2021 that Warriner was not mentally competent to stand trial. This means he either could not consult with his attorney with a reasonable degree of understanding, and/or he did not have rational or factual understanding of the legal proceedings against him.
Warriner did not receive legally mandated mental health treatment at a state facility until October 2023 due to state hospital staffing shortages.
He had legally regained competency by December 2024 and returned to the Denton County Jail to await further court proceedings.
Competency and insanity are two distinct legal findings.
The insanity defense focuses on the defendant’s mental state when they committed the crime. In contrast, competency focuses on their current mental state.
A defendant cannot be found not guilty by reason of insanity until they can understand the charges against them and strategize with their attorney.
“It seemed very clear from the moment I got on [this case] that this was an insanity case,” Warriner’s attorney Sarah Roland said in an interview Wednesday. “But because he was incompetent, we couldn’t raise that issue as a defense.”
After over seven years and three months since the killing, Judge Brody Shanklin held a hearing on Aug. 14 and found Warriner not guilty by reason of insanity. The finding states prosecutors did prove beyond a reasonable doubt that Warriner was guilty of the indicted offense: the murder of his 65-year-old mother, Sarah Ann Warriner. However, Roland proved that at the time of the murder, he did not understand his conduct was illegal due to severe mental illness.
“When a judge or jury finds somebody not guilty by reason of insanity … you don’t just walk out necessarily,” Roland said.
Isaac Warriner is still in the county jail as of Wednesday evening. He is still technically being held on charges from Cooke County, but Roland notified the Denton County Sheriff’s Office that they were dismissed because of the insanity finding in Denton County. The Sheriff’s Office will eventually transport Warriner to a maximum security state hospital. Once at the hospital, he will be mentally evaluated. The judge will review that evaluation and determine how long Warriner should be committed to the state hospital.
After the ordered period, Roland said the hospital would continue evaluating Isaac Warriner on a routine basis to determine if he still poses a risk to public safety or if he can be released back into society.
The outcome of Isaac Warriner’s murder case has been a long time coming, Roland said, after so much oscillation between his competency and incompetency.
“There is no doubt that languishing in jail is not a good thing for any person’s mental health, particularly those who are already compromised,” Roland said. “In cases like Isaac’s, a lot of times, the person is housed in a single-cell unit all day every day. It’s a very different environment than even being in a pod with other humans. So, it’s definitely not helpful to a person’s mental health.”
The heartbreaking part of the case, Roland said, is that there were ample opportunities for intervention before Warriner killed his mother.
The Denton Police Department received 12 calls from friends and family, between February 2019 and the week before the killing, asking for welfare checks and reporting domestic disturbances.
Two calls were made by Sarah Warriner, who reported arguments with her son.
In one instance, days before her death, she called officers to their apartment to report her son had cut his arms with a razor the day prior.
She told officers she took him to the hospital, where Sarah Warriner said her son told a nurse he was going to kill himself and then his mother.
The nurse called for security but he fled the hospital. Once Sarah Warriner arrived home, she told officers, her son took her phone and would not allow her to call anyone.
A nurse at Texas Health Presbyterian Hospital Denton told police that Isaac Warriner stated he wanted to harm himself.
“There were very clear opportunities to intervene and prevent this,” Roland said. “Multiple times, there were people in positions where it could have and should have been prevented.”
Then-Police Chief Frank Dixon told the Denton Record-Chronicle in May 2019 that authorities were aware for months that something was not right.
There was not much officers could legally do beyond report what they were told and what they observed, Dixon said, because a person has to accept treatment.
“At no time did he express to us that he was going to harm himself or anyone else,” Dixon said at the time.
Dixon later told the Record-Chronicle in October 2019 that the case prompted the department to assess how it tracks welfare concern calls and trains officers to recognize symptoms of mental illness for improved documentation and service referrals.