Detectives who need to park near courthouses now have to ask for permission if they want to use their unmarked cars, the Daily News has learned. The directive comes in the wake of revelations by The News that the NYPD has been towing unmarked cop cars, leaving detectives stranded with no way to transport suspects, witnesses or victims. The NYPD says the towing, carried out by traffic enforcement agents under the direction of the Internal Affairs Bureau, is necessary to prevent detectives from blocking hydrants and crosswalks and parking on sidewalks.