Police are using a 300-year-old law to prosecute gangs after violent attacks, including members who just stand by and watch.
Officers in London are targeting youth violence with the so-called Joint Enterprise law which allows them to charge any suspects present at an incident with the same offence as those directly involved.
It means a youth who encourages or watches another gang member kill someone could also be charged with murder.
Detective Superintendent Simon Morgan, of the Metropolitan Police, said: "Standing by is not a defence.
"Anybody and everybody that is involved in an incident of violence, we will look to identify them and if the evidence is there, we will look to prosecute them."
But the move has met criticism, including the Law Commission which warned it is being used to scoop up anyone present at the time of an attack instead of focusing on those responsible.
Professor Jeremy Horder, of the Law Commission, told the BBC Panorama programme: "It may be that only some members of the gang endorsed or encouraged or helped the killing, others did nothing of the sort.
"But they're all being scooped up in with it."
However Helen Newlove, whose husband Garry was beaten to death by a gang of youths, backed it.
One of the three convicted of his killing was Jordan Cunliffe, who has maintained his innocence saying he did not participate in the attack
But Mrs Newlove said: "Would you stand there watching somebody else kicking and punching? Would you actually think that was right to watch even if you didn't do the act? Because I certainly wouldn't. They were as guilty as the person doing the act."
The Met police is now warning youngsters in the capital of its tough stance with a tour and video presentation at schools and youth groups.