M (1931)
When the police in a German city are unable to catch a child-murderer, other criminals join in the manhunt.
The oldest film on the list (by a decent margin), and one that I wrestled with quite a bit as to whether or not I should include it in this list. Is it generally classified as "horror?" Not usually. Does it have enough horror elements that I think it can slip in? Absolutely. Child killers are horrifying. Child serial-killers are especially horrifying. And Pe