Killer Force (1976)

Bradley (Peter Fonda), a security officer at a diamond mine, plans to steal from the company in order to infiltrate a team of criminals that is planning a major heist. Meanwhile, tough enforcer Webb (Telly Savalas), who isn't aware that mine officials orchestrated the stealthy task, pursues Bradley with ferocity. After Bradley finally earns the trust of the jewel thieves, they begin to plan their operation, but his duplicity may end up costing him his life.