Jill Hennessy's twin sister, Jacqueline Hennessy, once played her sister's character during courtroom scenes filmed while Jill was unavailable, due to filming an appearance on Homicide, Life on the Street (1993).
The distinctive "thunk-thunk" sound effect used in between scenes was created by combining close to a dozen sounds, including that of a group of monks stamping on a floor. The sound is intended to be reminiscent of both a judge's gavel and a jail cell door slamming.
Prior to becoming an actor, Dennis Farina (Detective Joe Fontana) was a Detective in the Chicago Police Department for eighteen years. He got into acting through his former partner and police commander, Chuck Adamson, who had retired and became a police consultant on movies and television shows.
Steven Zirnkilton, who narrates the opening credit sequences, only appeared on-screen once. He played a detective in the pilot episode, Everybody's Favorite Bagman (1990). He had one line of dialogue: "Look at that. Do you believe these guys?".
Towards the end of the fifth season, executive producer Dick Wolf decided not to renew Chris Noth's contract, citing that the interaction between Logan and the similarly jaded Briscoe (Jerry Orbach ) lacked enough dramatic contrast. Viewers and critics were shocked at the dismissal of the most popular cast member at that time. Years later, Noth convinced Wolf to produce Omicidio a Manhattan (1998) to wrap up the story of Mike Logan, which Noth felt had been prematurely extinguished on the show. Noth returned again to revive the character for three seasons of Criminal Intent (2001).