Big Pot (1976)

A gang of robbers takes possession of a load of diamonds.. Only one of them, Mark Lemmon, is arrested and sentenced to life imprisonment. But before being captured, the gangster had managed to hide the loot in a sewer. Five years later, Mackenzie, an insurer, pretending to be a mafia boss, assigns three petty criminals to arrange his escape. Once free, Lemmon finds the booty but now he has to deal with his new 'partners'.