Clarence Darby

Clarence Darby is a villain in the movie Law Abiding Citizen where he murdered Clyde's wife and child. He got away with murder and spend only 3 years in jail instead of life and/or death row. 10 years later, Clyde gets his revenge on him, but cutting him into pieces and made him Darby die in a slow painful death.

After his death, Clyde went after the justice department for making a deal with Darby. Clyde destroyed most of the justice department.

This shows making a deal with a murder like Darby can be a big mistake. Darby doesn't deserve to live.