No reason is given as to why vice cops were assigned to work on a "serial stalker". It is possible because Crocket was once assigned to similar case. Vice cops are assigned to gambling, narcotics, prostitution, and illegal sales of alcohol. This should have been handled by either burglary or the FBI.
When Lieutenant Castillo meets Crockett and Tubbs in the police station parking lot to tell them they're off the case, Castillo sets his keys and coffee on the roof of his car, but leaves the keys there when he goes into the station.