Yes, I definitely think that police need powerful weapons. After all, they are the ones who are called in during a crisis. If a criminal has a AR-15, the police need that, too, to be able to defend innocent people. Most policeman just want to help, and they deserve to be safe.
No, the police do not need these weapons because their job is to protect people, not scare them. By operating the biggest guns, the community will feel separated from the people who are meant to the protect them. Police should be as open to meeting with people as possible; holding big guns won't create peace.
The United States is in a bad position when it comes to relationships between cops and civilians, and stuff like this is exactly why. Through terrible policies such as the war on drugs, we create an antagonistic relationship so both sides feel they are 'at war' with the other. And when you're at war, you have to outgun the enemy. The cycle of violence must be broken so we can once again trust law enforcement officers.
I do not believe that anybody, but military, should have access to these types of weapons. There are too many possible scenarios where things could go wrong. I know that they could have been beneficial in events that have recently happened, but overall I do not think that would benefit as much as have negative impacts.