
Also: "Carrying out the duties of a police or fire department are frequently classified as 'governmental' or 'discretionary'. Under the statutes and case decisions in most states, citizens cannot sue the government for negligently performing (or failing to perform) a 'governmental' or 'discretionary' function."
Plus: "The general rule is that governmental entities owe a duty to provide police protection to the public, but not to protect any particular individual"
source: Dial 911 and Die, by Richard W. Stevens
P.S. I apologize I provide a single source, but I personally haven't read too much on this topic, other than the book cited.