The parents of a Michigan teenager who shot dead four students have each been sentenced to 10 to 15 years in prison.

A seven-year sentence was recommended, but prosecutors asked for more.

James and Jennifer Crumbley, the first parents of a US school shooter to be convicted, appeared together for the first time in months at Tuesday's sentencing hearing.

Both expressed regret about their son's attack, as their lawyers pushed to minimise their prison sentence.

In a landmark case, jurors in separate trials found each parent of shooter Ethan Crumbley guilty of involuntary manslaughter earlier this year.

Judge Cheryl Matthews said that the expanded sentence of 10 to 15 years was "to act as a deterrent" and reflected the parents' failure to stop the attack.

"They [parents] are not expected to be psychic. But these convictions are not about poor parenting. They concern acts that could have halted a runaway train," she told the court.

"Opportunity knocked over and over again, louder and louder, and it was ignored."

The Crumbleys are eligible for parole after they serve 10 years in prison, but they cannot be held for more than 15 years if parole is denied.

Prosecutors had alleged that the pair had dismissed clear signs that their son's mental health had deteriorated, and noted that the parents had bought Ethan Crumbley the gun he used in the 2021 attack.

Their son was 15 when he killed four students with a semi-automatic handgun at Oxford High School. Seven others were wounded in the shooting.

He is now serving life in prison without parole.

On Tuesday, parents of the dead students, who were all under the age of 17, delivered emotionally charged victim impact statements in court.

Nicole Beausoleil, mother of 17-year-old victim Madisyn Baldwin, addressed Ethan Crumbley's parents directly.

"When you were purchasing a gun for your son and leaving it unlocked, I was helping her finish her college essay," a teary-eyed Ms Beausoleil said.

"You decided parenting wasn't a priority," she added. "And because of that I've lost my daughter."

Jill Soave - the mother of another 17-year-old victim, Justin Shilling - was the second parent to speak. She noted that her "horror and trauma is hard to put into words".

But she looked directly at James and Jennifer Crumbley as she slammed the parents for their "failure to act" and stop a "completely preventable" tragedy.

"If only they had done something, anything, to shift the course of events," she said.

In a separate trial for each parent, prosecutors accused the Crumbleys of ignoring warning signs about their son's growing mental health crisis. They accused them of being negligent by buying him a gun and not storing it properly.

Prosecutor's sentencing recommendations were based on four separate counts of involuntary manslaughter, one for each of the four students that were killed.

During Tuesday's sentencing, the prosecution said James Crumbley showed a "total lack of remorse" after they read from a profanity-laden transcript of a call he made from jail. They alleged that James Crumbley had made death threats against the lead prosecutor in the case during the call.

James Crumbley's lawyers disagreed, and said that their client only "vented" and used language that was "angry" and "not respectful".

The shooter's father emphasised his regret in a statement before the hearing and told the court later that he wished he had acted differently.

"I cannot express how much I wish that I had known what was going on with him or what was going to happen, because I absolutely would have done a lot of things differently."

Jennifer Crumbley also shared her own regret to the families affected.

"I stand today not to ask for your forgiveness, as I know it may be beyond reach, but to express my sincerest apologies for the pain that has been caused," she said in court

James Crumbley's lawyer, Mariell Lehman, said that there was no evidence that Ethan Crumbley's father was aware of his son's plans.

Defence attorneys also argued that there was no legal precedent for this case, and it was inappropriate to hold the parents responsible for each person that their son killed.

Prosecutors disagreed, as did the judge.

On the day of the shooting at Oxford High School in Oxford, Michigan, the Crumbleys cut short a school meeting about a disturbing drawing their son had made, instead opting to go to work and not take him home.

School staff later sent him back to class without checking his backpack, which contained the gun his parents had purchased.

An independent investigation published last year alleged multiple failures from the school system, including the decision to allow Ethan to return to class.

In response, the school district has pledged to review and improve its practices and policies. (Courtesy, excluding headline, BBC)

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