Sawed (2004)

When the residents of a small-town realise they are in grave danger due to a spate of serial killings, a group of teenagers decide to take the law into their own hands and hunt down the perpetrator. Ten years prior to these slayings, a young man named Devon was killed in a style that resembles the current outbreak of violence, leading to many suspicious whisperings breaking out, and the heroic teen's believing Devon may still be alive. Trying to solve two intertwined mysteries results in a frenetic race to the finale of the movie, with a genuinely surprising twist in the tale keeping viewers guessing right up to the bloody end.