The documentary shows how there were some really high level bank executives involved in libor frauds and that was getting media attention. Therefore, SFO met with banks and eventually, based on documents provided by the banks, decided to prosecute simple traders.
The reason traders have been sent to trial has nothing to do with the actual libor fraud carried out by executives. But since it is still about libor, has been sold to the media as the libor trial. Start and end date of the "crime" have been carefully chosen to not include evidence of the executive crimes (such as the phone call shown in the documentary). SFO experts have admitted during trial to lie in order to convict these traders.
Many of these traders were in their early 20s when the alleged crime happened. Germany, France, and EU have already said that it was not a crime at the time and rejected extradition.
I rarely felt as sad as after watching that documentary.