Blow Out (1981)
Directed by Brian De Palma

Film Synopsis

Jack Terry is a sound engineer who works for a film production company that specialises in horror films.  One day, he is recording some sounds in a park when he sees a car go out of control and plunge into a river.  Without a moment's hesitation, he throws himself into the river and manages to rescue one of the occupants of the car, a young woman named Sally.  He is too late to save the driver of the car, who happens to be a prominent politician.  Unwilling to implicate himself in a scandal, Jack agrees to say nothing about what he has witnessed.  But later, when he plays back the audio tape on which he recorded the tragedy, he hears two sounds that concern him.  One sound is unmistakably the noise of a car tyre bursting.  But before this he hears another, which sounds like a gun being fired.  Far from being an accident as he had supposed, it looks as if Jack has witnessed an assassination...