Luke Walmsley died from a single stab wound to the heart

Luke died of a single stab wound to the heart in the incident at Birkbeck School in North Somercotes, Lincolnshire, on Tuesday, say police.

A 15-year-old pupil is still being questioned by police in Skegness and the school remains closed.

Police will have to apply to a magistrate on Wednesday for more time, if the questioning is to continue.

Chief Superintendent Phil Carter of Lincolnshire Police told a news conference the incident happened at 1000 GMT in a corridor near the science laboratory.

Staff were the first to administer first aid to Luke, who was then taken to Grimsby Hospital by air ambulance but was pronounced dead about an hour later.

This is so out of character that it is almost unbelievable that it should happen at our school John Stevens, chair of governors

"We have recovered a knife, but are not prepared at this stage to issue a description of it," he said.

"We will begin interviewing pupils today using specially-trained officers," he said.

There were a number of pupils in the corridor at the time and officers will be speaking to those first in an attempt to try and find out exactly what happened.

Mr Carter described Luke as a "fun-loving lad" who was interested in sport and was fit and healthy.

"It is just a tragic waste of life," said Mr Carter.

The school will continue to remain closed while forensic examinations take place at the scene.

Police said they will liaise with the headmaster and education authority as to when the school can reopen.

John Stevens, chair of governors, said violence had never been an issue at Birkbeck.

Support offered

Mr Stevens said: "This is so out of character that it is almost unbelievable that it should happen at our school.

"Obviously there have been the odd occasions when there has been a little bit of, say, bullying, but there has never been anything of this scale, it has never worried us.

"There has never been any suggestion that we would have something so serious and devastating as this."

He said the priority was offering staff and students the support they needed.