When a crime is committed, the investigation is entrusted to an independent judge (both regarding the police and the state), called the “Investigating Magistrate” working from police investigations, evidence and testimony collected. He has to form his "absolute conviction" on the identity of the culprits, he has to conduct an investigation "to charge or discharge “, i.e. without any a priori about the guilt of a suspect.

Among the decisions he may take, he may issue an arrest warrant against a suspect, should he consider that there is against him - her "serious and corroborative evidence" of his – her possible guilt.

At the end of the inquiry, the Investigating Magistrate concludes a judicial decision: if the charges are not sufficient, he takes an order of dismissal (which stops the proceedings); otherwise, he takes an order of referral to a court named “Chambre d’Accusation” which then decides to refer to the trial court (Cour d’Assises). Appeal procedures are provided.

The decision to order detention of the suspect belongs to another magistrate, the “Judge of Liberties and Detention”: the detention comes into force at the request of the Investigating Magistrate, notably when the freedom of the suspect to act is dangerous for public safety or to gather evidence: That is the case when pressure can be exerted on witnesses, directly or indirectly by the suspect or his accomplices (subornation of witness

In the case of the murder of Sophie Toscan du Plantier, the execution of European arrest warrant and extradition of the suspect to France leads to "an indictment" of the latter, which include two important implications for defence:

- Firstly, access to the complete file of the investigation, under the same conditions as for “civil parties” (family of the victim).

- Secondly the presence of lawyer at all stages of the inquiry requiring the presence of the suspect: hearing, confrontation “face to face” of witnesses, etc.