There are some pretty basic expectations that most people have when watching a movie, namely the presumption that the steely hero will eventually triumph over the villain, right?
Studios typically like to send audiences home happy and fulfilled, confident that balance has been restored to the world and the tyrannical antagonist has been killed, jailed, or otherwise foiled.
But that's not always the case, and every so often filmmakers will be given the creative green-light to actually let the bad guy get away with their heinous actions.
It's a risky strategy that's liable to divide audiences - especially the multiplex popcorn gobblers - but can also result in far greater dramatic satisfaction than a shoehorned, often unrealistically happy ending.
These 10 films dared to let at least one of their antagonists live to fight another day, whether a fly-by-night schemer, a degenerate criminal, or an outright murderous psychopaths.
Rather than have such riveting characters killed or captured, these films all left them free to continue their villainous pursuits, granting them a certain cinematic immortality in the process...
10. The Zodiac Killer - Zodiac
David Fincher's masterful crime thriller Zodiac is fiercely committed to historical accuracy, and offers little in the way of a Hollywood ending for its based-on-true-events serial killer hunt.
The Zodiac Killer terrorised the San Francisco Bay Area from the late 1960s through to the early 1970s, murdering at least five people and alleging to have killed dozens more.
As in reality, Fincher's film never sees Zodiac brought to justice, concluding that suspect Arthur Leigh Allen (John Carroll Lynch) may have been guilty, yet Allen ultimately died before he could be questioned further in the case.
It's an agonisingly inconclusive ending to a story that has fascinated true crime fans for more than 50 years, and given how daringly Zodiac taunted both the police and obsessive newspaper cartoonist Robert Graysmith (Jake Gyllenhaal), it's somewhat fitting that he disappeared into the ether without a trace.
Naturally the chance of Zodiac still being alive, let alone ever actually getting caught, becomes more scant with each passing year. He won.