A teenage schoolboy accused of stabbing his teacher to death decided to knife her on the flip of a coin, it has emerged.

Serial troublemaker Sinan Y. returned to his school in Ibbenbueren, Germany, on 10th January after he was sent home for a day for bad behaviour.

And he sought out popular teacher Sabine K. and stabbed her over and over in a frenzied attack, say prosecutors.

Cold-blooded Sinan, 17, watched her bleed to death as he calmly called police and waited in the classroom to be arrested.

Victim Sabine, 55, died of blood loss before she could be taken to hospital.

The pupil later confessed to police that he decided to kill her on the flip of a coin, reported local media.

Senior public prosecutor Martin Botzenhard told local media on 9th February: “When he was arrested, the accused told one of the investigators involved in the operation that he tossed a coin and then made his decision.”

Accused Sinan has been exercising his right to remain silent ever since the killing.

His peers described him as quiet and a loner, telling how he hated all his teachers.

After he was sent home following “recurring conflicts with teachers”, he chose to take out his anger on widely-liked mum-of-two Sabine.

A student of Kaufmaennischen Schulen Tecklenburger Land earlier told local media: “I always looked forward to her lessons.”

Staff at the vocational school earlier told media: “Sinan was a classic type of bigot.”