Images of an 18-year-old being attacked by a gang of 40 youths in a busy London high street have been shown to jurors.
Mr Osman suffered three fatal stab wounds during the attack
The footage shows Mahir Osman being set upon by the gang who took less than a minute to kill him during the attack near Camden Tube station, north London.
The jury at the Old Bailey saw Mr Osman being punched, stamped on and stabbed 20 times on a Saturday night in January last year.
Eight defendants, including five youths, deny murder.
Faisal Wangita, 25, Ismail Mohamed, 18 and Liban Elmi, 20, all from north London, and five youths aged 16 to 17 who cannot be named because of their age, also deny three other charges of conspiracy to carry offensive weapons, wounding with intent to cause grievous bodily harm and violent disorder.
The attack involved two Somali gangs
Brian Finucane QC, prosecuting, said: "It is all over literally in seconds. He was set upon by a gang of up to 40 Somali youths. It lasted less than a minute."
He added: "I warn you, you are going to see footage of this young boy being murdered."
The court watched in silence as youths carrying wooden bats, bottles, hammers and knives assaulted Mr Osman.
He was left rolling about in the road as his attackers ran off and tried to get away on a number 253 bus before it was stopped by police, said Mr Finucane.
Some of the youths evaded arrest by climbing out of the bus's emergency exit at the back. An arsenal of weapons had been found in and around the vehicle, the court was told.
The attack had been the culmination of escalating violence involving two Somali gangs from Camden and the Tottenham-Edmonton area.
The trial was adjourned until tomorrow.