Visible crew/equipment: In one of the scenes where Arnold is running through piles of debris an explosion behind him causes him to fly through the air. The mechanism that launches him in the air can clearly be seen flipped up from the ground.
Visible crew/equipment: When Dynamo chases Arnold Schwarzenegger in his off-roader, Arnold lures him in/onto a pile of junk, following which Dynamos car crashes and overturns. When the car is on its side you can see the cable used to overturn the vehicle. In the next shot the cable has disappeared.
Visible crew/equipment: Just before Dynamo turns the car over, you can see several times that there is a stuntman driving the car.
Answer: They needed a scapegoat, someone to blame. The government controlled the people through violence, but at the same time tried to convince the people the government was fair (i.e. Runners who made it through were given their freedom when in fact they never left the arena alive). The people at Bakersfield were still massacred (that part wasn't made up) by the government in order to control the riot, but just not by Ben. But people would just riot more if they knew the government ordered their killing, so the footage was faked to make people think Ben acted alone and against orders. And to continue the ruse, they convicted him to appease the people and prevent them from rioting.
Bishop73