A 15-year-old youth has been given a life sentence for stabbing a student to death in a row over conkers.

Architecture student Steven Grisales, 21, died in August last year, after he challenged youths who were throwing conkers in their spiky husks at him.

He had been shopping for his grandmother and was on his way to Silver Street station in Edmonton, north London, when he was attacked in College Close.

The youth, who cannot be identified for legal reasons, denied being the killer but was found guilty of murder at the Old Bailey, last month.

Judge Richard Marks ordered that the youth be detained at Her Majesty's Pleasure with a minimum term of 10.5 years.

The defendant had been in court for robbery and burglary and was subject to electronic tag monitoring as part of a rehabilitation order imposed the previous month. The prosecution told the Old Bailey that the youth had removed the tag two days before but the incident happened before his 9pm curfew.

Judge Marks said his pre-sentence report made "grim reading" and mentioned two incidents with knives, one at school and the other involving his mother.

Andrew Edis QC, prosecuting, told the trial: "This was a sudden, unnecessary killing as a response to a confrontation which took place in the street, which was about nothing very much. It was about throwing some conkers. Horse chestnut trees in north London shedding their conkers, people picking them up and throwing them about."

Speaking outside court, Mr Grisales' parents said they had "no forgiveness" for their son's killer and that the sentence was not long enough. Andres Grisales said: "Ten and a half years for taking away our son, taking away his future, all of his plans. Everything was taken away from him - ten and a half years is a very short sentence.

"It was amazing to learn how many offences he had committed before this - violent offences, robberies. He broke his curfew so many times and nothing was done. There was no custodial sentence."