CSI: Crime Scene Investigation Season 5 Episode 22

After an exhaustive day, Catherine stops by a bar where she has a fling with another customer. As she is leaving, he gives her his number on the bar's match box. Later on that night, Grissom calls in for a favor as he is short on staff. A woman was murdered. Prior to her death, she was seen with the same man who was hitting on Catherine in the same bar. A similar match box with a phone number inside, found on the victim, further points to this man as the main suspect.