Buck, the cops weren't prevented from defending themselves, they protected themselves very well by hiding outside while the action was all inside. They were prevented from going inside to protect the students, for whatever reason. That particular failure shouldn't be allowed to stand as policy.
It's apparent that all you know about this came from ABC news or some similar source. Maybe you'd benefit from further reading.
No police department allows a policy of mistakes. These guys know their responsibilities and not just to the community. You are on a witch-hunt and you are going up a dead-end.
I suggest that you go after current government policy that destroys our precious rights and freedoms. Go after BIG_POLITICAL_MACHINES that say they support the Constitution and then they turn-around and tear it up because, "it's the will of the people."