Born Killers (movie, 2005)

John and Michael are taught by their father at a young age that people are merely piggy banks... if you need money, just break one open. Charming and brilliant, they roam the country robbing and murdering anyone foolish enough to get in the car with them. After their partnership becomes strained and John sets off on his own, he discovers his father had a secret family... another wife and a daughter in another state. With a renewed sense of purpose he sets out to find and kill his stepsister. But this may be more challenging than he thinks... has he met his match?