While in prison, Richard Kuklinski claimed to be responsible along with four other men for the kidnap and murder of former Teamsters union boss Jimmy Hoffa on July 30 1975 in a restaurant parking lot in Detroit. The five-man team were allegedly given the contract on Hoffa by Tony Provenzano, a captain in the Genovese crime family. Kuklinski claimed to have been paid $40,000 for the hit. Kuklinski said that he knocked Hoffa unconscious with a blackjack and, while holding Hoffa's chin up, thrust a hunting knife into the back of his head. Hoffa's body was then allegedly placed in the trunk of a car that was then crushed and sold as scrap metal to Japanese car makers. The claims only surfaced after Kuklinski's death in March 2006 in a book by author Philip Carlo and will probably never be substantiated.
Apart from a 15 second flashback, the film makes virtually no mention of the awful childhood that Richard Kuklinski endured. His parents were both deeply violent people, with his father accidentally beating his older brother to death. This contributed to Kuklinski becoming a very violent person himself. The film completely glosses over the fact that he regularly beat his own wife.
To aid her performance as the oblivious wife, Winona Ryder removed all the pages of the screenplay that didn't involve her.
Michael Shannon was able to emulate the real Richard Kuklinski's voice by listening to TV interviews and the HBO documentary, The Iceman Tapes: Conversations with a Killer (1992).
James Franco and Benicio Del Toro were originally cast in the lead roles. Franco was replaced by Chris Evans and Del Toro was replaced by Ray Liotta, although Franco was given the brief role of Marty Freeman instead.