Detective Munch’s backstory had him as a Baltimore cop before he moved to NY. Somehow NBC and Fox agreed to have him play his role as Baltimore PD Detective Munch in a flashback episode of the X-Files. The original character of Munch was on the show “Homicide: Life on the Street”
https://en.wikipedia.org/wiki/Homicide:_Life_on_the_Street
Great show IMO.