Honeymoon Killers, The
The Honeymoon Killers is a 1970 film directed by Leonard Kastle that tells the true story of Raymond Fernandez and Martha Beck, who, in the late 1940s, conned and murdered several women using "lonely hearts" ads in local papers. Their story would also be told (inaccurately) in the 2006 film Lonely Hearts.
Interestingly, the film was going to be the first feature film for Martin Scorsese, but the way he directed the film made it impossible to edit, so Kastle (the writer of the film) was brought on to direct.
The following firearms were used in the film The Honeymoon Killers:
During the murder of Delphine Downing (Kip McArdle), Raymond Fernandez (Tony Lo Bianco) tells Martha Beck (Shirley Stoler) that Delphine keeps a pistol in her drawer, which turns out be be a Röhm RG-10 revolver. Martha uses it to shoot her in the head. This is probably the model used in the film's poster (shown above).