A churchgoing teenager who who was also the head of a South London gang was sentenced to life imprisonment yesterday for the murder of a schoolboy rival.

Adu Sarpong had been to a Bible class with friends hours before a bloody street battle with a rival gang in which he stabbed Alex Kamondo, 15, with a kitchen knife.

Sarpong, 18, who was convicted at the Old Bailey, was the leader of K Town Crew, which clashed with Kamondo’s gang, Man Dem Crew, in Kennington in June. Up to 30 youths fought with knives, hammers, metal bars, bottles and a samurai-style sword.

The trouble began when Kamondo, whose street name was “Little Alien”, joined others in taunting and insulting their rivals on the Ethelred estate in Kennington, where they had gone to make a revenge attack on K Town Crew after a brawl among younger gang members that day.

Sarpong, known as “Fame”, armed himself with the knife and rounded up his gang. He then challenged the rival gang, one of South London’s most notorious, asking: “What you doing in our area?” Kamondo, who had posed for gang website pictures with a sawn-off shotgun, told Sarpong: “You don’t own these estates.”

In the fight that followed, Sarpong plunged the knife into Kamondo’s chest with so much force that it broke a rib and the handle snapped off. Kamondo, who lived on the nearby Kennington Park estate, suffered a single 20cm stab wound that pierced his left lung and heart.

Sarpong fled but was arrested shortly afterwards. He told the Old Bailey that he had been “pumped up with adrenaline” and heard someone cry out that he had been stabbed behind him, but did not see the stabbing. However, his finger-prints were found on the murder weapon and he was picked out at a series of identity parades by members of the opposing gang.

After the killing, Kamondo’s father, Kamondo Mulumba, released a picture of his son dying in hospital and said that he had been doing his GCSEs at Kingsdale School in Dulwich, southeast London and was looking forward to college. He said: “Alex loved music and was doing his exams at school. He wanted to go to college and do electrical engineering.”

Mr Mulumba, a father of six who brought his family to London from the Democratic Republic of Congo in 1991 when his son was three, also wrote an emotional victim-impact statement that was read to the court. It said: “My sanity is at the brink of breaking down, but for the sake of my living children, life must go on. We will just have to trust the authorities to defend and revenge my son’s death. That way he fights from the grave and we hope that justice will be served for a child killed in cold blood with such venom.”

Sentencing Sarpong to youth custody for life, Judge Gerald Gordon, QC, hit out at teenage knife culture, telling him: “The blow must have been inflicted with severe force because it dissected one of his ribs, before entering his heart and it broke the blade from the handle.

“His death brought tragedy to his family and once again a court has heard from a distraught relative that the family will never recover. That’s the almost inevitable consequence of taking a life, particularly a young life. It’s the carrying and use, often as we hear for minuscule motives, of such knives that is causing death and devastation to families and that has got to be stopped.”

Sarpong, of Kennington, will serve at least 14 years before being considered for release. He smirked and looked up at the gallery as he was led from the dock.

Times Recommends

• How I lost the gift of joy for a while
• Why Ann Widdecombe has got it wrong
• Alas, it’s the end of the road for petrolheads