The Cybernetic Autonomous Remote Barricade or C.R.A.B. is one design concept that will never be. The concept will never make it not so much because we can't build robots as much as because the police would never pay for something so cool.
I think this might be the child of that robot from Robocop that looked like a giant microphone and could think but not walk down stairs. The concept comes complete with a smoke screen and the ability to emit gas to break up crowds. My son has that last ability too.
The concept has six legs and would be an all terrain robot killer that is apt to go on a shooting spree. You can check out the video below to see more of the designer's vision for the robot. Now I have to go rent Robocop.