Thrillers often overlap with mystery stories but are distinguished by the structure of their plots. In a thriller, the hero must stop the plans of an enemy rather than uncover a crime that has already happened. Mystery thrillers also occur on a much grander scale: the crimes that must be prevented are serial or mass murder, terrorism, assassination, or the overthrow of governments. Jeopardy and violent confrontations are standard plot elements in the mystery-thriller genre (i.e., Triangle), unlike in the mystery genre where the story is more downbeat and dramatic (i.e., Changeling).
While a mystery climaxes when the mystery is solved (i.e., Gosford Park), a mystery thriller climaxes when the hero finally defeats the villain (after reveal), saves his own life and often the lives of others (i.e., Oldboy). There is very little violence, menace and threat in mystery/detective films (especially between the villain and other innocent people), whilst the violence is quite intense in thrillers and the villain is more ruthless. In thrillers influenced by film noir and tragedy, the compromised hero is often killed in the process.
A thriller isn't just about someone being murdered. There is always something bigger and more important at stake behind the murder that may endanger more lives. Where in a mystery the motive for a crime such as insurance fraud can be greed, in a thriller mere money doesn't come across as believable for all the terrible things the antagonist will do.