Catherine was born in Las Vegas, where her mother, Lily Flynn, worked as a cocktail waitress and a showgirl. She spent most her of life thinking that her biological father, wealthy casino owner Sam Braun, was only a friend of the family, and she only found out about truth when she was already an adult working as a crime scene investigator. Prior to earning her Bachelor of Science degree in Medical Technology from the University of Las Vegas, Catherine had been employed as an exotic dancer and was, for a short period of time, addicted to cocaine.

Her marriage to the late Eddie Muggs was riddled with conflict and problems, and after their divorce, their relationship did not change for the better. When Eddie was murdered, Catherine’s relationship with their daughter, Lindsey, was also affected. Lindsey became rebellious and distant, and in an effort to straighten out her daughter, Catherine took her to the morgue and showed her the body of a person who was murdered. Later, she placed Lindsey in a private school that would discipline her harder.

As an important part of the night shift crew of the Las Vegas crime lab, Catherine has established strong relationships with her fellow investigators. She is supervisor Gil Grissom’s right hand woman, but their professional bond was once tested when she accepted some money from Sam, who had been occasionally involved in cases under investigation. She also maintains friendships with the younger CSIs, namely Nick Stokes, Warrick Brown (with whom she flirted briefly), Sara Sidle and Greg Sanders.

Her relationship with her father, Sam, often created conflict with regards to her line of work, but when he died in her arms after he was shot in front of his casino, she expressed her grief and love for Sam by lighting one candle in a Roman Catholic church.