Randall Cooper was an exterminator who killed whatever his brother needed killed. Detached and almost tool-like, Randall wasn't all there as a person.
The most human-like thing about the man was his love for Tammi Peyton. His x-ray vision allowed him to watch her all the time. He saw something in her that she didn't see in herself. This love would be what led him to turn on his brother.
For months, his twin brother Dwight Cooper had been ordering Randall to help him kill local drug dealers for their money. When Carlton Chase was thought to be skimming, Randall was sent to dispatch him as well. This death in a police station, led the FBI to investigate and the scheme of Dwight Cooper to begin to unravel. When the choice came for Randall Cooper to pick between his brother and Tammi Peyton, Randall chose Tammi. He knew she had lied about coming back to take Randall with her when she fled with the money she had embezzled but he still wouldn't kill her. He murdered his brother instead and allowed himself to be taken in by the FBI. Sitting there in the police station he looked through the walls to see Tammi's face on a computer monitor. (TXF: "Surekill")