He believes a great deal of information can be discerned by what music a person has on his or her MP3 playlist (episode 517, "A Grizzly Murder"). He had a good relationship with the Crime Lab personnel and also the CSI's up until the season 6 episode "Bang, Bang, Your Debt," when it is discovered that he's stolen and used a credit card that belonged to the late Tim Speedle, to the outrage of Delko and Calleigh, who told him to turn himself in or she would issue a warrant for his arrest.
Presumably, this instance of identity theft was the final nail in the coffin for Cooper and ended his career at the lab, prompting him to resign from the lab for good and also in disgrace. As a result, he holds a personal grudge against Calleigh for this, despite the fact that she doesn't press charges, and steals the flashcard out of her camera at a crime scene to put the pictures on a website which he has created to "take her down a notch."
He also changes her cell number and posts it on the site and she is kidnapped from a "lead" (episode 615, "All In"). After an enraged Delko confronts him, Cooper later feels remorseful and turns in evidence that helps the team track down Calleigh, free her and arrest her kidnappers.
He was replaced by Dave Benton.
Cooper was played by Brendan Fehr.