Cops are extremely limited in their rules of engagement, largely to try to avoid situations like this. The individuals get frustrated by these rules, so it isn't fair to target the cops on scene, it's a lose lose situation. Imagine being a cop in the 60 seconds before he caused that carnage. What do you do? Fire a shot, miss and hit someone on the other side of the street? Fire a shot, hit and the car crashes into a crowd? T-bone the car, which then runs into a crowd? Attempt to block him in, aggravating the farkwit, causing him to do exactly what happened. At the speed these things go pear shaped, it's nigh on impossible to take out a vehicle cleanly and safely. Terrible terrible situation.