Im starting an idea for a twisted crime-noir graphic novel set in the 20s-60s. Whats good source material?

Hello. Recently a friend and i over the course of a few months were having a ideas about a 40-60s set period piece with a twist: a psycholical thriller about a mob-enforcer-turned-vigilante on the trails of a brutally murderous crime faction masquerading as a well-functio ning, long-lasting traveling cross-country 'circus/lounge' act, where lines of loyalties are tested, characters are immensely textured, a richly stark portrayal of moral depravity, a sprawling timespan, and the ultimate notion of their being 'no good vs evil, but only good and evil in of itselves'. It was recently where we decided this would be a great anthology for graphic novel material. For the time period we wanted to go for the whole crime noirish and vividly lush darkness sorta like SIN CITY exibited, but just our own idea. But to be honest, we arent professionals but merely dreamers. What we would like to know is what standout books, authors movies, or pop art would help educate and shape our vision for our 'crime noir' idea? Thanks