This shocking footage shows the moment a teenager was stabbed to death in a row on a night bus in London.

Roree Cox, 18, knifed 14-year-old Kevin Ssali to death after intervening in an argument between his younger brother and the victim.

The footage shows Cox, dressed largely in black with a dark baseball cap, boarding the bus.

He takes a knife from his shoe. The footage then cuts to show several people, including Cox, walking upstairs on the bus.

As two people walk in front of the camera, Cox has reached up from the stairs and stabbed his victim once in the chest.

Kevin, wearing a short-sleeved white t-shirt is seen clutching at the fatal wound at the top of the stairs.

In the attack on September 15 2012, Cox jumped from one bus to another at a set of traffic lights after receiving a phone call from his brother, Chay, telling him of the latest row between him and Kevin, with whom the brothers had a "history of antagonism".

When he boarded the 202 after swapping from the 261 in Lee Green, south east London, Cox pulled the knife and ran up to the top deck in search of the unarmed victim.

Police said the attack lasted "no more than five seconds." Cox killed Kevin with a single blow.

The attacker immediately fled the scene and ran away, and his victim died in hospital the following day.

He was described by grieving family members and friends as an "angel" with an unforgettable smile.

Speaking after Cox was found guilty of murder, Detective Inspector John Marriott said: "The events that led to Kevin's death started as an exchange between two boys that wasn't violent, or threatening to other people on the bus.

"Roree Cox's actions show a young man who was carrying a knife, and prepared to use it. He stabbed Kevin without even considering if his brother was in danger or if Kevin, who was unarmed, could fight back."

Cox, of Southwark, was found guilty of murder at the Old Bailey yesterday and will be sentenced on February 28.