Cannibal Ferox (1981)

New York grad student and anthropologist Gloria, her brother Rudy, and their friend Pat, travel to a remote part of the Amazon jungle to find and disaprove the local theory of cannibalism among the local tribes when they run into something far worse: a cruel and sadistic, streetwise drug dealer, named Mike Lawson, and his partner, Joe, hiding out in the jungle from murder and drug-dealing charges in back in New York and whom are presently using the docile natives to mine for emeralds and harvest cocca. When the crazed Lawson kills a few natives, including the daughter of the chief, just for his sadistic enjoyment, the warriors turn against their masters and subjuect the two dealers and three grad students to the most horrific torture and murder for their crimes using their own harsh law of the jungle.