Las viboras cambian de piel

The name of this movie is Las viboras cambian de piel released in 1974-05-23 and it's main theme is Rene Cardona Jr.'s bloody Mexi-Western is the story of a hired gun that wants to complete his last big job so he can retire with his prostitute. The job consists of killing a sheriff who keeps himself hidden away inside an old monastery. A series of double crosses culminates with an excessively bloody Wild Bunch inspired massacre inside the monastery..