Sociologist and researcher Dr Jarrod Gilbert told the Herald gang members stayed well clear of the police and justice system when it came to crimes committed against them.
Gilbert, who wrote Patched: the history of gangs in New Zealand, said anyone caught stealing off the Mongrel Mob could expect street justice in brutal retribution.
"The gangs tend to forgo the criminal justice system.
"If someone steals a car the ordinary course of action is to go to the police and get it sorted out through the justice system.
"Gangs will take care of it themselves and bypass state channels," said Gilbert.
"They mete out a punishment in the same way the state does but do it by their own measure."
He said that usually involved violence or paying a tax.
While he had no way of knowing its veracity, Gilbert said he would not be surprised if it wasn't authentic.
The sickening post on the Facebook page The Bro Hub has now garnered more than 257,000 views in a matter of hours.
