Michigan school shooting: Suspect, 15, charged as an adult

The suspect in a Michigan school shooting will face charges of terrorism and first-degree murder following a rampage that left four students dead and seven injured.

Prosecutors on Wednesday charged Oxford High School student Ethan Crumbley, 15, as an adult.

Police have not yet specified a motive for the attack.

The victims were named as Tate Myre, 16, Madisyn Baldwin, 17, Hana St Juliana, 14, and Justin Shilling, 17.

Announcing the charges on Wednesday, Oakland County prosecutor Karen McDonald said evidence showed the suspect had planned the attack "well before the incident".

"This isn't even a close call," she said. "This was not an impulsive act."

Ms McDonald said the teen will face one count of terrorism, four counts of first-degree murder, seven counts of assault with intent to murder, and 12 counts of possession of a firearm, with further charges likely as the investigation unfolds.

At a later news conference, Oakland County Sheriff Michael Bouchard said charging the suspect as an adult was "the most appropriate" action.

"I agree with holding this individual wholly and completely responsible for the deplorable, tragic event that occurred by his choice," he said.

Police have requested that the suspect be transferred from a juvenile detention centre to the local county jail.

The teenager has refused to speak with investigators on the instructions of his family.

The sheriff stressed that the teenager had never been on the radar of law enforcement or the school. He also added there was no evidence the suspect had been bullied by his peers.

"There is nothing that he could have faced that would warrant senseless, absolutely brutal violence on other kids," said Mr Bouchard.

Investigators have found the suspect loaded his firearm - purchased by his father on Friday - in the bathroom and then walked through the hallway firing more than 30 shots from the weapon.

Tate, Madisyn and Hana died on Tuesday, while Justin was confirmed dead on Wednesday.

Among those admitted to hospital, a 17-year-old female student remains in critical condition with a gunshot wound to the chest.