The Honeymoon Killers (1969)

Based on the true story of Raymond Fernandez and Martha Beck, who met through a lonely-hearts correspondence club. Ray is weedy, feral, and untrustworthy; Martha is enormous, compulsive, and needy. Together, they play out a horrifying scheme in which he lures lonely women out on dates and proposes marriage to them, with her pretending to be his sister. They take the women's savings and then murder them remorselessly. Dank, claustrophobic, and weirdly engrossing, this movie never quite gives in to the comforts of conventional narrative. Francois Truffaut named it as his favorite American film.