UK Guardian article about Cillian - includes a mention of Dunkirk:
https://www.theguardian.com/film/2017/mar/12/cillian-murphy-it-is-getting-absurd-with-the-dumbing-down?CMP=twt_gu

Guns also feature in Murphy’s next big-budget outing, the Second World War picture Dunkirk, which sees him reunite with director Christopher Nolan. Nolan had considered Murphy for the lead role in his 2005 Batman reboot. In the end, the job went to Christian Bale, but Nolan selected Murphy as the villainous Scarecrow instead, covering those much-coveted icy blue peepers with a burlap sack. He also cast him in 2010’s Inception.

Though Nolan’s films are usually shrouded in secrecy, as Murphy points out: “Everybody knows what happened at Dunkirk, so it can’t deviate too much from the facts. It is not like Inception or Interstellar, there’s no major reveal.” He describes Nolan as an old-fashioned filmmaker. “And while all of his films have big budgets and involve a lot of set pieces, they always feel like a little independent film for the actor because you only ever have one camera and Chris watches on a tiny little monitor. He is right there beside you.”