12 Unsolved Movie Mysteries That Drove You Mad

2. Who Killed Mildred's Daughter? - Three Billboards Outside Ebbing, Missouri

Martin McDonagh's Oscar-winning drama follows Mildred Hayes (Frances McDormand) as she seeks justice for the rape and murder of her daughter (Kathryn Newton) seven months prior.

Later in the movie Officer Dixon (Sam Rockwell) investigates a man from Idaho who he overhears speaking of raping and murdering a young girl in a similar manner. However, between him being out of the country during the killing and passing a sneaky DNA test with flying colours, he's not their guy.

The film never in fact reveals the real murderer, and ends with Mildred and Dixon taking a road trip to kill the Idaho man given that he has very clearly raped and killed somebody.

The prevailing theory is that the killer might well be Mildred's ex-husband and Angela's father, Charlie (John Hawkes), who is shown to have an interest in young women and a tendency to get violent when drunk.

But like Inception, the ending seems to be concerned less with the finer details of who and what, and more with what it says about the characters of Mildred and Dixon.