On pain of nullity, the authorisation given pursuant to Article 706-81 shall be issued in writing and must be specially reasoned.
It mentions the offence or offences that justify the use of this procedure and the identity of the judicial police officer under whose responsibility the operation is taking place.
This authorisation sets the duration of the undercover operation, which may not exceed four months. The operation may be renewed under the same conditions of form and duration. The magistrate who authorised the operation may, at any time, order its interruption before the expiry of the fixed duration.
The authorisation is placed in the case file after completion of the undercover operation.