A jury has found the mother of a Michigan school shooter guilty of involuntary manslaughter, after failing to stop her son from carrying out the deadly attack.

Jennifer Crumbley, 45, was charged on four counts of involuntary manslaughter on Wednesday (AEDT), with each carrying a maximum sentence of 15 years.

The verdict marks the first time a school shooter’s parent has been convicted of manslaughter over a mass shooting carried out by their child.

Prosecutors accused Crumbley of being “grossly negligent” in allowing her son, who was 15 at the time, to have a gun, and ignoring warning signs of his mental health issues, and getting him proper treatment.

“It’s a rare case that takes some really egregious facts,” Oakland County Prosecutor Karen McDonald said in closing arguments Friday, before jurors began deliberations in the case that could shape future criminal liability for US parents.

“It takes the unthinkable, and she has done the unthinkable, and because of that, four kids have died.”

Crumbley’s defence argued the blame lay on her husband for improperly securing the firearm, and for failing to notify the school about her son’s behavioural problems.

Crumbley’s husband, James, is facing a separate trial on the same charges in March. He has pleaded not guilty.

Her 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.

Taking to the stand in her own defence, Crumbley expressed no regret for her actions.

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

“It was very difficult,” one member of the jury said following the verdict, according to NBC. News.

“Lives hung in the balance and we took that very seriously.”

That juror said their decision took account of the fact that she was the last adult to handle the weapon.

“The thing that really hammered it home was that she was the last adult with the gun,” the juror said.

Ethan Crumbley, now 17, is serving life in prison without parole for killing four classmates at Oxford High School in November 2021.

His mother’s sentencing hearing is set for April 9.