First, some (probably most) states have laws that prohibit suits againts the state for damages due to such things.

Also, there have been court cases where a person asked for police assistance, assistance did not show up or came very late and bad things happened. Courts have held that the government or its agents have no obligation to protect an individual. If I understand the concept right, a government agency's function is to provide for the general welfare of citizens, not to garentee the saftey of every individual.

At leat that is the way I understand it. I could be wrong.