Red herring: an idiom referring to a device which intends to divert the audience from the truth or an item of significance.
— The American Heritage Dictionary of the English Language
In procedurals, these are the people interview, talked with or just shown to confuse the audience as to who is really the killer or person of interest.
Most commonly, the first appearance of a “red harring” will be within the first major interview scene. While the detectives are talking with someone, the camera may pane slightly away from the central action to another person within the scene. Alternatively, the character being interviewed may be seen to look over toward or away from the detective frequently. (TV “science” had taught us that when people lie they will move their eyes away from the person and then back. e.g. looking “shifty”)
“Red harrings” may also appear during the big “Ah! Ha!” moment of discovery in the episode. Right when the main characters have it all figured out, some new piece of evidence will be produced that will throw their theories (and the audience’s) out the window. This is the most classic example. While the audience has been led to believe it might be someone, a new person will be introduced to cast doubt.