At the risk of politicizing a recent tragedy (something that the other side doesn't mind doing), it is commonly thought that police presence has a deterrent effect. Generally, that may be true for some crimes.
But, when it comes to extremely violent crimes, that deterrent effect is reduced to the point of non-existence. The guy that got pulled over and took some shots at the IMPD officer didn't care that he was a police officer (or maybe, that was the reason).
Police play an important role in society. But, they cannot guarantee the safety of any particular person in any particular place at any particular time. In fact, they are legally not liable for any such protection.
Amen. Rep as soon as I can. Ambushes are now becoming a new thing. Gone is the sacred feeling that you don't screw with the police. Groups now wait for officers enmass to attack.