Washington (AFP) - A US jury began deliberations on Monday in the high-profile case of a Michigan mother charged with involuntary manslaughter over a school shooting carried out by her teenage son.

Jennifer Crumbley, 45, and her husband, James, 47, are the first parents of a school shooter to face felony charges in the United States for the actions of their child, according to prosecutors.

Ethan Crumbley, 17, their son, is serving a life sentence for the November 30, 2021 shooting at Oxford High School which left four students between the ages of 14 and 17 dead.

The Crumbleys are accused of buying their son the 9mm SIG Sauer handgun he used to carry out the shooting and ignoring warnings he had mental health struggles.

James Crumbley is to be tried separately in March.

In closing arguments Friday, prosecutor Karen McDonald urged the 12-person jury to find Jennifer Crumbley guilty of four counts of involuntary manslaughter -- one for each victim.

Crumbley failed to "exercise ordinary care when the smallest, tragically simple thing could have prevented it," McDonald said.

"She could have asked her son where the gun was. She could have locked the ammunition. She could have locked the gun," McDonald said. "She could have told the school they had just gifted him a gun.

"She could have told the school about her son being in crisis previously and asking for help."

Defense attorney Shannon Smith countered that Crumbley cannot be held accountable for the actions of her troubled son.

"No one could have expected this," Smith said. "Can every parent really be responsible for everything their children do?

"And this clearly was not foreseeable to Mrs Crumbley because there's no one in the world, including Mrs Crumbley, who would let a school shooting happen," Smith said.

"This case is a very dangerous one for parents out there," she added. "It just is. And it is one of the first of its kind."

'Wish he would have killed us instead'

Crumbley testified during her trial that her husband bought their son the gun just days before the attack as an early Christmas present, and she took the boy to a shooting range the next day.

She said her husband was responsible for storing the weapon at their home, and it was for her son "to use at the shooting range only."

Crumbley told the jury she never had any exchanges with her son's teachers about discipline issues, although he frequently failed to hand in homework assignments and his grades were poor.

Asked about their relationship, Crumbley said: "I thought we were pretty close. We would talk. We did a lot of things together."

She said she never had reason to believe her son was capable of carrying out such a violent act.

"As a parent, you spend your whole life trying to protect your child from other dangers," Crumbley said. "You never would think you have to protect your child from harming somebody else.

"I wish he would have killed us instead," she said.

The Crumbleys were summoned to the school on the day of the shooting after a teacher was "alarmed" by a violent drawing she found on Ethan's desk.

The parents were shown the drawing and advised they needed to get the boy into counseling.

They allegedly resisted taking their son home and he returned to class.

He later entered a bathroom, emerged with the gun which had been concealed in his backpack and fired more than 30 shots.

The father of an Illinois man accused of killing seven people in July 2022 pleaded guilty in November to misdemeanor charges of "reckless conduct" for helping his son obtain the assault rifle used in the mass shooting.

A conviction for involuntary manslaughter carries a maximum sentence of 15 years in prison.