A Michigan judge has decided not to consider the affairs the mother of the Oxford school shooter had in her and her husband's upcoming trial as the first parents in the U.S. charged in a mass shooting.

Jennifer and James Crumbley are due in court Wednesday, days after their son, Ethan, was sentenced to life in prison.

The judge in the case also said evidence of Ethan Crumbley's bird-torturing hobby, including storing a bird's head in a jar under his bed, will be inadmissible in the trial against his parents.

Oakland County Circuit Judge Cheryl Matthews held that the so-called "bird evidence" is irrelevant, but noted that "even if it were relevant, it is unfairly prejudicial."

Prosecutors had hoped to use the "bird evidence" against Jennifer Crumbley, who along with her husband, have separate trials on involuntary manslaughter charges for buying their son, Ethan, the gun that he used in the massacre and not disclosing that to the school when they had the chance to.

Four students were killed in the shooting. Six others and a teacher were also injured.

Mom's knowledge of troubled son's bird behavior

From the start, prosecutors have laid much blame for the tragedy on the Crumbleys, portraying them as selfish parents who cared more about their horses and getting drunk than taking care of their troubled son. Specifically, prosecutors allege the parents ignored a child who was spiraling out of control and hallucinating, and instead of getting him help, they bought him a gun, which he used to carry out the Nov. 30, 2021, massacre.

As for the bird evidence, the prosecution disclosed new details about Jennifer Crumbley's knowledge of her son's bird interest. For example, on May 3, 2021, Ethan Crumbley took a picture of an unmutilated bird and posted it on his Instagram page with the following text: "How do you do fellow bird."

A month later, his mom responded "Dead," with an emoji of a person with hands raised up.

Similar pictures of the same bird and a nest were found on Jennifer Crumbley's phone, the prosecution wrote in a Dec. 7 filing, arguing the jury needs to see a "complete picture" of the bird evidence at the mother's trial. The prosecution also wanted jurors to know about the photograph of a bird's head in a jar that Ethan Crumbley took on May 15, 2021.

But the judge said no, granting the wish of the defense, which previously argued:

"The 'bird evidence' is so extremely disgusting, sickening and appalling that its admission would certainly inflame the passions of a jury. The jury will undoubtedly judge Mrs. Crumbley for the heinous acts of her son, which she knew nothing about," defense attorney Shannon Smith wrote in a previous filing.

Evidence that will and won't be allowed

Smith also expressed concern about prosecutors bringing forward an alleged affair the mother was involved in when Ethan was 6 years old.

The judge concluded no affairs would be admissable as evidence. The judge is also not allowing in trial any mention of the parents' messy house, alcohol and marijuana use in the home, their son's internet searches and a Nazi coin he kept.

But the judge will allow evidence about the time and money the Crumbleys spent on horseback riding and their son playing violent video games.

More recently, the judge also admitted as evidence an Instagram account by Ethan Crumbley that his mom followed.

While the shooter kept multiple Instagram accounts, one included a photo of the gun his dad bought him during a Black Friday shopping trip in 2021, just four days before the shooting.

After getting his gun, Ethan Crumbley took photos of it and posted it to Instagram, writing: "Just got my new beauty today. Sig Sauer 9 mm."

His mom had access to that account.

Four days later, after his parents were summoned to his school over a troubling drawing he had made in math class, Ethan Crumbley emerged from a bathroom and opened fire with his new gun.

The prosecution argues that the Crumbleys, more than anyone else, could have prevented the shooting had they disclosed to the school that they had bought their son a gun days earlier. But they withheld that information after being shown a drawing their son had made of a gun, a bleeding body, and the words, "The Thoughts won't stop, help me." The couple asked whether their son could be returned to class, went back to their jobs, and promised to get their son help in the coming days.

The Crumbleys maintain they had no way of knowing their son would carry out a school shooting, and that the gun at issue was safely stored.

Ethan Crumbley pleaded guilty to all charges

Ethan Crumbley, who was 15 years old when he carried out the shooting and later pleaded guilty to all the charges, did not ask for leniency at his sentencing last week. Rather, he told the judge to give the victims what they asked for, and that only he — no one else — was responsible for the tragedy.

The teenage killer also made a disclosure that could help his parents, whom prosecutors say engaged in gross negligence that contributed to the deaths of the four slain students.

"We are all here because of me today, what I did ... I could not stop myself," Crumbley told the judge at sentencing. "My parents did not know what I planned to do. They are not at fault."