A group of teenagers celebrated after carrying out a murderous knife attack on a 19-year-old man after he gatecrashed a girl's 16th birthday party, a court has heard.
Lewis Blackman was stabbed 14 times after being chased from the rented flat in Kensington, west London, having arrived uninvited after invitations were circulated on social media.
Six boys, including four 17-year-olds and two 16-year-olds, are on trial at the Old Bailey accused of his murder and causing violent disorder in the early hours of February 18.
The court heard on Wednesday that the birthday girl hoped about 50 boys and girls her own age would be at her party - at a flat rented through website Airbnb.
She was careful to only invite guests from the Hackney area of east London and particularly keen to avoid inviting any boys from Camden as she knew there was a "history" between young men from the two areas, jurors were told.
Despite her best efforts, Mr Blackman turned up as part of a group of ten young men from Camden, in north-west London, after the invitations were circulated on social media - mainly Snapchat.
He was armed with a knife while his friend had a firearm when they tried to force their way into the party, causing damage and forcing some guests to flee "in terror", the court heard.
CCTV cameras caught a larger group of party-goers, some also armed with knives, chasing Mr Blackman along the residential streets of Earls Court.
Prosecutor Oliver Glasgow QC said: "He was stabbed, he fell to the floor and he was then set upon. The brutality of the attack, which saw him stabbed a total of 14 times as he lay defenceless on the ground, is truly shocking.
"What is perhaps even more disturbing is the apparent celebration that his killers enjoyed after he had been fatally wounded and the calm and carefree manner in which they walked away."
Mr Blackman died at the scene after suffering multiple stab wounds, including two to the chest.
"It is the Crown's case that, no matter what may have been said or done by Lewis Blackman or any of his friends to offend or frighten the guests at the party, there is nothing that any of these six defendants can say to excuse the murderous attack upon him," said Mr Glasgow.
"The first four defendants were all armed with knives and each of them took part in the attack. They chased down their target, they produced their knives and they butchered him.
"The last two defendants were part of the chasing group. However, they did not physically attack Lewis Blackman, but they encouraged their friends to carry out the attack and celebrated in its success afterwards."
All of the teenagers deny the charges and the trial continues.