While horror makes wild claims of “based on a true story” from time to time, not every instance seen in the genre is a gimmick formed from a shred of truth. Quite the opposite is 2016’s Lake Bodom (a.k.a. Bodom), a film based on a well-documented true story — a true crime, in fact. The real-life inspiration for this offering of Finnish horror also has the distinction of being a famous cold case; from a legal standpoint, the Lake Bodom Murders were never solved. And it is in that room for speculation that Taneli Mustonen’s film found its story.

Lake Bodom has all the right ingredients for a typical slasher: teens, camping, the woods, and most importantly, a killer. And for that first portion of the film, that is exactly what Mustonen and co-writer Aleksi Hyvärinen delivered. Using a tragedy plucked from local history as its backdrop, the...