OAKLAND, Michigan - A Michigan teenager on Monday pleaded guilty to murder and terrorism charges in a mass shooting last year that killed four of his classmates and wounded more than half a dozen other people.

Ethan Crumbley, 16, is accused of opening fire at Oxford High School on Nov 30 last year with a semi-automatic handgun that his father purchased for him as a Christmas gift days before the massacre.

The case appears to be the first in the United States in which the parents of a teenage school shooter have been charged with crimes attributed to their child.

“Ethan Crumbley’s guilty plea is one small step forward on a long path towards obtaining full justice for our clients. We will continue to fight until the truth is revealed about what went wrong leading up to this tragedy,” Mr Ven Johnson, a lawyer representing several families of the victims, said in a statement.

Ethan, who was a 15-year-old at the time of the shooting, pleaded guilty in Oakland County Circuit Court to 24 charges, including one count of terrorism causing death and four counts of first-degree murder.

Two boys, aged 17 and 16, and two girls, aged 17 and 14, were killed, while six other students and a teacher were wounded in the rampage at the school, located outside Detroit.

Ethan was also charged with seven counts of assault with intent to murder and 12 counts of possession of a firearm in the commission of a felony.

Prosecutors told the court there was no plea agreement with Ethan, who faces life without parole when he is sentenced. A tentative sentencing hearing is scheduled for Feb 9, 2023.

The massacre was one of dozens of shootings in US schools that caused death or injury this year alone. One of the deadliest took place in May, when a gunman killed 19 children and two adults in Uvalde, Texas.

On Monday, around the same time that Ethan entered his plea, at least two people were killed and six wounded or injured when a shooter opened fire at a St Louis high school, according to the city’s police commissioner. Officers then fatally shot the suspect.

At the Michigan hearing, Ethan wore an orange jumpsuit and a white mask over his nose and mouth while his left hand remained shackled. As he stood at the podium, he answered “yes” to a series of questions the judge and prosecutor asked him, confirming his guilty plea.

Ethan’s lawyers on Monday withdrew an insanity defence notice that they had previously filed with the court.

His parents James and Jennifer Crumbley have pleaded not guilty to involuntary manslaughter charges connected to the shooting.

In that case, Rochester District Court Judge Julie Nicholson said evidence showed they had bought a gun for their son despite signs that he was a troubled young man.

Four days before the shooting, Ethan accompanied his father to a gun shop, where James Crumbley bought a 9mm handgun, prosecutors said. REUTERS