The 4th Season 1 episode "Dawg Days" was actually the third to be filmed, and guest director Stephen Gyllenhaal had real trouble establishing the proper look and characterization, only having the pilot episode to go on as a reference point. Gyllenhaal and Michael Chiklis in particular disagreed over how unsympathetically Vic Mackie should be played, with Chiklis' view winning out. The decision was made after this that the writer of the episode would always be on set to assist the director and actors.
Jay Karnes is fluent in Spanish, but during the episode "Dawg Days" it was creator Shawn Ryan's idea for Karnes to have his character butcher the Miranda Rights as he read them in Spanish.
Catherine Dent kept accidentally calling guest star Sticky Fingaz by the less flattering name Stinky Fingaz.
The recording studio scene, the off-duty police security at the club, and the shady police interaction, are direct references to Rampart division's real-life notorious "C.R.A.S.H." squad in the late 1990s, which was in league with Death Row records, which was affiliated with the Bloods street gang. There was strong evidence that a number of police officers were connected to the murder of rapper Notorious B.I.G.