The Cold Killer(1967)

Original title: Uccideva a freddo

Jose Desmet, a butler, killed his employer because the latter, once a district judge, had long ago condemned Desmet's father, a well known gangster, to death. When Desmet tries to seduce Salazar's daughter, who is heir to a goldmine, kills a woman and the village doctor because they had found out that he was selling weapons to the Indians, a government investigator, Bill Walcome, together with the sheriff, sets out to put an end to Desmet's activities.