Other mistake: Just before Arnold arrives at his brother Edward's apartment, he walks across a plaza. Note the people standing/sitting in the background, along the railing. They are still there, apparently not having moved an inch, in another scene of that plaza which is supposed to be much later after Arnold has been caught, sent to the tele-station and gassed unconscious. (00:14:20 - 00:26:20)
Other mistake: When everyone in the audience and everybody at the betting board see the original unedited version of what really happened at Bakersfield, it shows a soldier hitting Ben with the butt of his weapon from Ben's point of view, which is an impossible camera angle. And as it's the original unedited footage, it won't be something they faked.
Other mistake: When Killian's guard goes to enter his code to open the gate, it starts to open when he touches the first digit, rather than after the last digit.
Other mistake: In the opening sequence of the Huey flying over the crowd, the uniforms of all five men stay unruffled, despite the doors and windows being open, which would allow the wind to pass through.
Other mistake: The list of possible prisoners contestants the computer goes through shows different information, but the page with the 8 rows of double letters and numbers remains relatively the same, even though it's suppose to show variations and different information (i.e. AA always has -583 and -5483 and BB always has -484 and -4838).
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