Frank McCarthy was a corrupt detective, serial killer, and pedophile who appeared in season CSI: Crime Scene Investigator.
Frank was a cop with PD and had a daughter named Amy. He was partnered with another cop, Dennis Graves, and they eventually met a man named Michael Keppler. Michael was going out with his daughter Amy and the two eventually got engaged. Then for unknown reasons, in 1985 Frank raped his own daughter, who later commited suicide, and later blamed it on a man named Kevin Reeder. Frank was going to kill him but Mike got to him first, executed him and gave the gun to Frank, presumably tp dispose of. Unbeknownst to him, Frank held on to the gun and kept it stored for the future.
later Frank and Mike and bonded over the grief of losing Amy and Frank used the money he was saving for Amy's future to further Michael's carrer in law enforcement. They would later help Dennis Graves when he would kill suspects in his cases and they would cover it up. Mike then letf Trenton and left Frank and Dennis to carry out their work. Later Dennis was indicted for the murders Frank got worried. He hatchet a plan to take him to Vegas so that could kill him.