What people fail to understand is the police are not required to protect you from being harmed by someone with a gun. The Supreme court ruled that citizens have no legal expectation of protection from the police. The police are best at gathering evidence after the crime has been committed and then they start looking for the murderer. Protection is ultimately your responsibility, not the police, who might be late answering that 911 call for help.
Justices Rule Police Do Not Have a Constitutional Duty to Protect Someone
http://www.nytimes.com/2005/06/28/politics/28scotus.html?_r=0