Dramatic footage of boys fighting with knives in a McDonald's, causing an innocent elderly woman to be knocked to the floor, can be seen for the first time.
The incident took place in April last year in Penge, south east London - just five months before one of those present was involved in stabbing 17-year-old Kyle Yule in the street in Gillingham, Kent, on October 6.
The footage is released as a 16-year-old boy was stabbed in another branch of the chain in Ipswich, Suffolk, on Wednesday.
It comes as the number of offenders dealt with by the criminal justice system after being caught with knives or offensive weapons has reached the highest level in seven years, according to Government
The findings were released amid concern about a surge in knife violence, particularly in London.
The CCTV captured in Penge shows teenagers with knives race into the takeaway, attempting to stab each other, and continue to fight in the doorway and outside on the pavement.
Amid the fracas, Tyler Ralph, of Hertfordshire, slashes a bystander's head and pushes an elderly woman pulling a shopping trolley to the floor, a court heard.
Aged just 16 at the time, he was convicted of assault occasioning actual bodily harm, affray and possession of a blade for the incident.
Judge Adele Williams drew attention to his history of violence with knives - he was also convicted for possession of a blade in 2014 - when she sentenced him at Maidstone Crown Court on Thursday to detention for life with a minimum term of 16 years after the murder of Mr Yule.
She told the court how he and his four other co-defendants all regularly carried knives, and videos of Ralph found on his phone showed him with a "fearsome array of knives and weapons".
In other footage, which can now be published, he films himself picking up with a gloved hand an array of weapons laid out on a bed, and brandishing a sword.
All of the footage was shown in court to a jury weeks ago as part of the trial but the press were prevented from publishing it until now.
A court order continues to prevent the press fully identifying Ralph and any of his fellow co-defendants who are still under the age of 18.
They can now be named, and the town in which they lived reported, but their faces must be obscured in any images or footage used and their street address must not be published, Judge Williams said.
Initially the media were banned by the court from publishing footage in a separate ruling after police declined to release it.
Judge Williams relaxed restrictions after both orders were challenged by reporters.