A judge has acquitted a mentally ill Stillwater man who fatally stabbed his father from behind as his sister watched and tried to halt the killing.

William James Scheel, 32, killed 59-year-old William Mark Scheel in July 2016 in the family's home while acting on "delusional beliefs [and] had no appreciation of the nature or wrongfulness of his acts at the time of the stabbing," Washington County District Judge John Hoffman wrote in a ruling last week that followed a bench trial earlier in October.

Hoffman concluded that by reason "of his active mental illness at the time of the event, [the defendant] is excused criminally from his conduct in this case."

Defense attorney Marsh Halberg said Tuesday that "bottom line, there were three experts who all either directly or indirectly said he was not competent at the time of the death. There were no opposing expert opinions" presented to the judge.

The elder Scheel died on July 8, 2016, from "significant stab wounds in the back of his neck" after the attack at the residence on Mulberry Street, according to the second-degree murder charge.

The defendant was hospitalized shortly after the killing with stab wounds of his own that were inflicted by his sister, who used a knife in trying to stop the attack on their father.

While at the hospital, the son told a doctor that he had not been taking his medication for some time, according to court records.

The younger Scheel was under civil commitment for schizophrenia and living in a group home. He had been ordered to receive medication by injection, but recently was allowed to administer his own medication even though the family knew he had a history of not taking it, the criminal complaint said.

The son resides in the state's secure mental health facility in St. Peter.