Michigan school shooting: Ethan Crumbley, 15, charged with terrorism and murder of four teens

A 15-year-old gunman who killed four fellow pupils in a school shooting in Michigan had reportedly posted a countdown on social media and written "Now I become death - destroyer of worlds" the day before the attack.

The suspected gunman was later identified by police as Ethan Crumbley, a bespectacled schoolboy.

Crumbley was charged with four counts of first-degree murder and one count of terrorism causing deaths.

The FBI is looking into the social media activity of the teenager as they seek to establish a motive for the shooting at Oxford High School near Detroit on Tuesday.

Six other pupils and a teacher were also injured.

It was the latest in America's decades-long string of deadly school shootings, with over 50 people injured or killed this year.

The teenager used a 9mm semi-automatic handgun his father had purchased four days earlier.

Before the attack he had posted a picture on social media of the gun and a target.

Police said it was believed he brought it into school in a backpack and then emerged from a bathroom and opened fire.

It was not believed that he was targeting particular individuals.

He had seven bullets remaining when he surrendered to police in a hallway.

Sheriff Michael Bouchard said: "That interrupted what could have led to several more victims. The way I see it is, there were seven more victims in that gun."

Those who died were Tate Myre, 16, Hanna St. Julian, 14, Madisyn Baldwin, 17, and Justin Shilling, 17.

Myre, a promising high school American football player, died in a police car on the way to hospital after trying to disarm the gunman.

In a statement fellow pupils said: "Tate is not just a hero to his fellow students at Oxford high school but a legend.

"His act of bravery should be remembered forever and passed down through generations."

Fellow pupils suggested the gunman had been "picked on" and bullied. He was refusing to cooperate with police after the attack.

Sheriff Bouchard said: "He was shooting people at close range, oftentimes towards the head and chest. It's just absolutely coldhearted murders."

The sheriff said at least 30 shots were fired.

Aiden Page, a pupil who barricaded a classroom door, said: "We grabbed calculators, we grabbed scissors, just in case the shooter got in and we had to attack them."