Eric Hainstock took two handguns into school

John Klang, 49, was shot in the head, chest and leg as he confronted an armed 15-year-old pupil who entered the school in Cazenovia on Friday morning.

A district attorney said the teenager, Eric Hainstock, was in custody and had been charged with murder as an adult.

Reports said Eric Hainstock had been warned by Mr Klang for having tobacco. He had also complained of being teased.

Mr Klang was shot as he wrestled the student to the ground after he confronted him in the entrance to the Weston school.

Hainstock, who armed himself with two handguns taken from his parents' home, could face a life sentence if convicted.

Witnesses quoted by local media said the assailant was armed with a shotgun and a .22-calibre gun.

'Weird in the head'

Student Shelly Rupp, 16, said she heard five shots and ran out of the school, but turned around and saw Mr Klang as he was shot.

"He was laying on the ground in the hallway. He had just a pile of blood by his leg," she told the Associated Press news agency.

Ms Rupp described the assailant as a first year student at the school. She said he had few friends and was "just weird in the head".

"He always used to kid around about bringing things to school and hurting kids," she said.

The incident came just days after a man broke into Platte Canyon High School in Bailey, Colorado, and took six female students hostage.

The gunman shot and killed one of his hostages before turning the gun on himself.