Masked gangsters goaded rivals by filming a drill rap about murder – from prison.
Footage was recorded on a mobile in a cell at London’s Pentonville jail.
Rappers believed to be members of the Wood Green Mob posted it to Snapchat.
A 75-second clip then went on YouTube – where it has been seen more than 300,000 times.
Sources say the rap is about the 2018 unsolved shooting of Kelvin Odunuyi, 19, outside a cinema in Wood Green.
Jen Lock, of Lives Instead of Knives, said: “It’s a mockery of justice.
"People go to prison for murder but are able to produce music.”
Wood Green thugs have waged a 10-year turf war with Tottenham gangs that has left at least four people dead.
Mobiles are illegal in jails and drill rap is blamed for fuelling violence.
The Ministry of Justice said: “Prisoners found with mobiles will be punished.
"We have requested that the video is removed urgently.”
