(CNN) — Jennifer Crumbley, the mother of the teenager who killed four students at an Oxford, Michigan, high school in 2021, was found guilty Tuesday of all four counts of involuntary manslaughter in a novel legal case that stood as a test of the limits of who’s responsible for a school shooting.

The jury of 12 deliberated for more than 10 hours. Jennifer Crumbley looked down at her clasped hands as the verdict was read. She was taken from the courtroom in shackles.

Crumbley, 45, had pleaded not guilty to the charges in the November 30, 2021, mass shooting at Oxford High School, in which four students were killed and six students and a teacher were wounded. She faces up to 15 years in prison, and her sentencing hearing was set for April 9. She has been behind bars since her arrest in a Detroit warehouse days after the shooting.

The prosecution argued Jennifer Crumbley is responsible for the deaths because she was “grossly negligent” in giving a gun to her son Ethan, who was 15 at the time, and failing to get him proper mental health treatment despite warning signs. Over a week of testimony, law enforcement officials, school employees, shooting victims and those who knew Jennifer Crumbley testified for the prosecution.

“It’s a rare case that takes some really egregious facts,” Oakland County Prosecutor Karen McDonald said in closing arguments Friday. “It takes the unthinkable, and she has done the unthinkable, and because of that, four kids have died.”

However, the defense argued the blame lay elsewhere: on her husband for improperly securing the firearm; on the school for failing to notify her about her son’s behavioral issues; and on Ethan himself, who planned and carried out the attack on his own. Defense attorney Shannon Smith said the case was “dangerous” for parents everywhere.

“Can every parent really be responsible for everything their children do, especially when it’s not foreseeable?” Smith said in closing arguments.

Jennifer Crumbley took the stand in her own defense and, in a remarkable moment, expressed no regret for her actions.

“I’ve asked myself if I would have done anything differently, and I wouldn’t have,” she testified.

Closing arguments took place Friday. The judge instructed the jury on the law Monday morning and deliberations followed.

Broadly, the prosecution’s case relied on an unusual and novel legal strategy and represented an attempt to expand the scope of blame in mass shootings. And in its specifics, the trial has provided an intimate view of the collapse of one American family in a tangle of sex, violence and mental illness.

Crumbley’s husband, James, is scheduled to go on trial on the same charges in early March. Jennifer Crumbley’s defense and the prosecution were barred from speaking publicly about her case until the end of James Crumbley’s trial.

Their son Ethan pleaded guilty to one count of terrorism causing death, four counts of murder and 19 other charges related to the deadly rampage. He was sentenced last year to life in prison without parole. He did not testify in this trial, as his attorneys said he would invoke his Fifth Amendment right to silence.

What happened in the trial

The prosecution’s case against Jennifer Crumbley has focused on three main aspects: her knowledge of her son’s mental issues, how he got access to the firearm and her actions at a pivotal school meeting on the morning of the shooting. Prosecutors sought to portray her as an inattentive mother, more interested in her horses and her extramarital affair than her son’s well-being.

First, the prosecution alleged she knew or should have known about Ethan’s deteriorating mental health issues. For example, he sent a series of texts to her in the spring of 2021 in which he said there was a ghost or devil in the house and pleaded for her to respond, but she did not do so. He also texted a friend that he had told his parents about the hallucinations and asked for help but his mother laughed at him.

However, in her testimony, Crumbley said the texts about a ghost were just Ethan “messing around,” part of an ongoing joke about their house being haunted. She also said his text to a friend was false and he had never actually asked for help.

“I thought we were pretty close. We would talk. We did a lot of things together. I trusted him, and I felt like I had an open door and he could come to me about anything. I felt as a family the three of us were very close,” she said.

Second, the prosecution accused Crumbley of gifting a gun to her son and improperly storing it. Surveillance video shows she and Ethan went to the gun range and took turns shooting on November 27, 2021, days before the shooting. “Mom & son day testing out his new Xmas present,” she wrote afterward on social media.

“The shooter was given the murder weapon by his parents, and this parent is sitting here on trial today,” McDonald said in her closings.

But in her testimony, Crumbley testified that safely storing the gun was her husband’s responsibility. “I just didn’t feel comfortable being in charge of that,” she said. “It was more his thing, so I let him handle that. I didn’t feel comfortable putting the lock thing on it.”

Finally, the prosecution highlighted her inaction in a meeting with school employees the day of the shooting. That morning, a teacher found a drawing from Ethan showing a gun and a person bleeding along with the phrases “the thoughts won’t stop help me,” “blood everywhere” and “my life is useless.” The Crumbleys were called into school for a meeting, and a school counselor testified he recommended the parents take their son home from school to get immediate mental health treatment.

The Crumbleys declined to do so that day because they didn’t want to miss work, the counselor testified, so the group agreed to keep Ethan in school for the rest of the day. They also did not mention to school employees that they had just purchased him a new gun or his previous hallucinatory texts. Shortly after the meeting, the teenager took a firearm out of his backpack and opened fire on classmates, killing Hana St. Juliana, Tate Myre, Madisyn Baldwin and Justin Shilling.

“Just the smallest of things could have saved, could have helped, Hana and Tate and Madisyn and Justin,” McDonald said. “Just the smallest of things. And not only did she not do it, she doesn’t even regret it.”

However, the school dean testified he did not view the drawings as threatening, though he also said he did not know and was not told that Ethan had access to a firearm and had been having mental health issues. Jennifer Crumbley testified the school meeting was “nonchalant” and “brief.”

“We agreed that it might stress him out more to do his school remotely the rest of the day. But there was never a time where I would refuse to take him home,” she testified.