FERGUS FALLS, Minn. — A Pine River, Minn., man who claimed hallucinations led him to believe a family he lived with worshipped Satan likely understood it was wrong to kill a woman and her son, a judge opined before ruling the defendant can’t use his mental illness as a defense.

William Lynn Hillman, 24, will be sentenced in late January for the deaths of 42-year-old Denise McFadzen and her son, 21-year-old Dalton, at their mobile home in Frazee, Minn., Otter Tail County Judge Kevin Miller determined Monday, Nov. 30. Hillman faces 40 years in prison for the two second-degree murder charges.

The ruling comes almost three years after the mother and son were found bludgeoned to death on April 17, 2018, at their rural Frazee, Minn., home. Prosecutors argued Hillman used a pipe wrench to kill the two.

Hillman told investigators he blacked out and didn’t remember what happened, according to court records. He has schizophrenia, a diagnosis that was used to determine he was not criminally responsible for attacking and threatening to kill his mother in April 2016.

Hillman’s defense failed to prove that his mental illness prevented him from understanding that killing Denise and Dalton McFadzen was wrong, Miller said. While several doctors determined Hillman qualified for the defense, evidence and a doctor's evaluation suggest he planned the killings, lied about blacking out and tried to tell doctors what he thought would make them believe that he wasn't culpable, Miller opined.

“Regardless of whether defendant thought that his actions were justified, he clearly understood the nature of what he was going to do and eventually did,” Miller wrote in the 26-page opinion.

Ruling reveals more about killings

The ruling presents more details about how Hillman came to live with the McFadzens, as well as what led up to the killings. It is the last of a two-part trial to determine Hillman's fate.

Miller found Hillman guilty in June during the first phase of the trial. In both parts, the judge looked at evidence and mental health evaluations without a trial or witnesses testifying in court, per Hillman's request.

According to the opinion:

Hillman was friends with the McFadzen children for most of his life. The family allowed Hillman to move in after the assault on his mother so he could “get a job and get back on his feet.” Andrew McFadzen, who is Dalton McFadzen’s cousin, helped him get a job at a turkey farm.

Hillman lived with Mark and Denise McFadzen, who shared their mobile home with their sons, Zachary and Dalton. A third son, Dillon, also lived in a mobile home on the property, while Andrew McFadzen lived there in a recreational vehicle.

There were reports of Hillman acting strangely, including spending time out in the cold and being withdrawn. The night before the killings, he asked Zachary McFadzen for a Bible.

Hillman, who admitted to not taking his medication for five months, told police he believed the McFadzens worshipped evil, and he said he felt unsafe. He said he couldn't remember what happened, but he said he knew he did a “bad thing” when he came to his senses, according to investigators.

“I just felt like I had to,” he told another doctor, according to the court filing, when explaining why he killed Denise and Dalton McFadzen. “I thought they were Satan worshipers possessed by demons trying to get my life source.”

However, he later revealed that he didn’t black out, according to the opinion. One doctor became skeptical of Hillman’s stories once he started recalling details of the killings.

“(I)t appears that defendant was building upon new knowledge of what a mental illness defense would look like and what information he would need to provide in order to be successful with the defense,” Miller wrote in citing that doctor’s opinion.

Miller noted that Hillman appeared to plan the killings to some extent. He waited until Mark McFadzen went to work before bludgeoning the mother and son, according to the court filing. He also locked the dog in an RV, Miller wrote.

Hillman then shut Dalton McFadzen’s bedroom door before attacking him in the victim’s bed, Miller wrote. Denise McFadzen’s body was found outside.

The judge said he doesn’t doubt that Hillman suffered from schizophrenia at the time of the deaths. Miller hinted that Hillman may have tried to go after Zachary McFadzen but was unable to due to the latter locking his door.

“These behaviors indicate that defendant was taking steps to avoid being caught or stopped,” Miller wrote. “The natural inference being that defendant knew what he was doing.”

Furthermore, Miller suggested that Hillman was targeting certain family members instead of trying to kill all of them. He didn't go after Mark, Andrew or Dillon, according to the court filing.

“Defendant may have believed that the McFadzens were devil worshippers or were possessed, there is no indication that he did not understand that they were still human,” Miller wrote, adding as soon as 20 minutes after the killings, he "admitted to doing something bad."