Police are for cleaning up crime scenes after the fact and trying to catch the people responsible. There's almost nothing they can do before a crime is committed. Even if a crime is in progress, they're more interested in protecting their own skin than in protecting yours. (Ever notice that a dead cop is a tragedy and a dead civilian is just another day at work?) I've known people who were attacked around the corner from a police van and the police did nothing, if they even bothered to notice at all.
Actually, police have no duty to protect individuals. The Supreme Court and lower courts have ruled this repeatedly.