A teenage killer has been jailed for life for the murder of Highgate schoolboy Martin Dinnegan.Joseph Chin, 16, has been ordered to serve a minimum of 12 years for stabbing 14-year-old Martin in the back on June 26 last year.

A teenage killer has been jailed for life for the murder of Highgate schoolboy Martin Dinnegan.

Joseph Chin, 16, has been ordered to serve a minimum of 12 years for stabbing 14-year-old Martin in the back on June 26 last year.

Martin’s murder came after violent clashes between his friends had and another group of youths earlier in the evening.

He had tried desperately to run from his attackers and had screamed please help me’ at horrified passers-by.

Chin’s friend Kevron Williams, 17, was also ordered to serve four years behind bars after being convicted of attempt to cause grievous bodily harm.

Passing sentence judge Brian Barker told Chin: “The fact is this was a vengeful attack out of all proportion to what may have gone before and no mercy was shown.”

At the time of the killing Chin was still the subject of a 12-month supervision order and was being monitored by the probation service.