Mark Palfreyman, 29, who led a gang known as the Greenwood Boys, got involved in an argument with Liam McCaffrey in a pub.
Palfreyman decided, with "chilling arrogance", that 18-year-old McCaffrey should be executed as punishment for crossing him and ordered his gang to carry out the killing.
Two hitmen, Raphael Smith and Daniel Jacobs, were driven to Bryony Close in Wythenshawe, where they believed McCaffrey was attending a hou
se party.
When Ashley Bowman arrived at the house wearing a hooded top, they mistook him for McCaffrey and Smith opened fire with a sawn-off shotgun.
