Besides accusations of heavy-handedness and abuse of preventive detention, critics accuse Mr Bruguiere and his colleagues of not giving defendants a fair chance.

BBC: Profile: France's top anti-terror judge

Two of the four men are to remain in preventive detention.

BBC: A French soldier patrols a street in Paris, 15 January

In France, no form of preventive detention is available for offenders under the age of 16, except for the most serious crimes (rape, murder, armed robbery).

ECONOMIST: France

These include strong federal preventive detention and anti-money-laundering laws.

BBC: Will India's security overhaul work?

For years, the police have been complaining that they can do little to control hooligans when no form of preventive detention is available for anyone under 16 other than for the most serious crimes (murder, rape, armed robbery).

ECONOMIST: France

If the court finds Breivik insane, he cannot be sentenced to prison or preventive detention, but can be confined to a psychiatric institution for the rest of his life, pending reviews of his mental state by the court every three years.

CNN: What will happen to Norway's mass killer Breivik?

But the court could also sentence Breivik under a provision called "preventive detention, " which also has a maximum of 21 years but can be prolonged in five year increments after that -- which means the court can detain Breivik indefinitely after his sentence if he is found to be a continued threat to the public.

CNN: What will happen to Norway's mass killer Breivik?