It's been a sanctuary city for years--no one has changed it. Bloomberg, Giuliani, Dinkins... I believe it first became a sanctuary under Ed Koch.
however, if an illegal is the victim of a crime or a witness to a crime, no action is to be taken against that illegal.
basically, if you commit a crime all bets are off. the feds, however, will not waste their time on anything less than a major crime committed by an illegal. i have literally had feds hang up on me saying they were not interested.