Detective 1st Class Mac Taylor, played by Gary Sinise, is the leader of the CSI team. The death of his wife, Claire, in the 9/11 attacks troubles him to this day. He served in the USMC, once saying that he had wanted to serve the country more than anything else in the world. He served in Beirut in 1983, which he still has a scar over his heart from. Mac has a close friendship with Stella Bonasera and plays bass guitar at jazz clubs during his off time.
Detective 1st Class Stella Bonasera, played by Melina Kanakaredes, is absolutely devoted to her job. She is often referred to as the 'Statue of Liberty', due to her strong personality, determination and intelligence. She is a half-Greek, half-Italian orphan, who grew up moving throughout foster homes. She is very close to Mac and constantly worries about his physical and mental well-being. After discovering that her boyfriend Frankie had secretly taped them making love and uploaded the footage to the Internet, she broke off their relationship. She was forced to kill Frankie in self-defense after he stalked her and held her hostage in her own apartment.
Detective 2nd Class Danny Messer, played by Carmine Giovinazzo, is considered the most complicated character of the show. Growing up on Staten Island in an "Italian Mafia" family under surveillance (As hinted at in Episode - 'Tanglewood'), he formed his own set of hybrid ethics, caught between the world of lawbreakers and lawmakers. Mac personally selected Danny for his team, an honor and a responsibility that he attempts to live up to each day. He is a very suspicious person; though he gets along well with the rest of the CSI team, Flack is the only person he truly confides in. Danny played minor league baseball until he got into a bar fight and broke his arm, which steered him towards becoming a CSI. Danny's brother Louie is in a coma after being beaten up by the Tanglewood gang (his brother was able to get a taped confession clearing Danny of a murder charge). Danny also has a budding friendship with crime lab newcomer Lindsay, who he affectionately calls "Montana."
Dr. Sheldon Hawkes, played by Hill Harper, formerly a Medical Examiner with the NYC Office of the Chief Medical Examiner (OCME), was a child prodigy who graduated college at eighteen, and by 24 he was a fully board-licensed surgeon. However, after losing two patients, he abandoned surgery in favor of the medical examiner's office. At the start of season 2, Hawkes has moved from the autopsy room out into the field.
Detective 1st Class Don Flack, played by Eddie Cahill, comes from a long line of law enforcement officials. He is the one that bridges the gap between old school NYPD and the new generation of CSI. He is the witty homicide detective who has very little patience with the "bad guy", and his technique is considered somewhat borderline, though nevertheless effective. He is good friends with Danny Messer, always willing to lend an ear to Danny's problems (As in the Episode - 'On The Job'). During the season 2 finale, Flack was severely injured in a bomb explosion. As the episode (and season) ended, he was still in a coma.
Detective 3rd Class Lindsay Monroe, played by (Anna Belknap, season 2 - ), a forensic scientist from Montana, who transferred in at Mac's request after Aiden Burn was fired. She joined during episode "Zoo York". Danny teasingly calls her "Montana," which annoys her, but Sid points out that Danny calls her that because he is harboring a crush on her. She has become good friends with Stella, who has given her some advice about living and working in the big city. Lindsay is known for Midwestern manners, such as taking off her shoes before entering a suspect's house. Despite being a newcomer to the crime lab, she seems to work well with the rest of the team. She takes her work seriously, especially when cases involve victims from small towns.
Detective Aiden Burn, played by (Vanessa Ferlito, season 1-2). Aiden was a Brooklyn native who has the ability to adapt to new situations very quickly. She was dismissed from the team in season two, episode 2 "Grand Murder At Central Station" after becoming obsessed with a rape case and considering planting evidence to implicate a suspect. She did not actually plant the evidence, but broke the seal on an evidence packet, throwing her credibility into question. Because of this, Mac felt he had no choice but to fire her to preserve the integrity of the CSI lab. Aiden agreed with his decision to fire her because she didn't know if she would resist the temptation in the future. After her dismissal from the crime lab, Aiden was apparently working on getting her private investigator's license while she was trying to bring down the rape suspect in the case that haunted her. In the penultimate season 2 episode "Heroes", she was ambushed and murdered by the rape suspect D.J. Pratt and incinerated inside a stolen car. In the heat of the moment, she left behind critical evidence that she knew would help her former colleagues close in on the perpetrator. Aiden's murder devastated Mac and the rest of the team, particularly Danny, to whom she was especially close.