The former head of France's anti-drugs agency, François Thierry, is being investigated on suspicion of complicity in drug-trafficking, prosecutors say, reports the BBC.
Mr Thierry ran the agency, Octris, between 2010 and 2016.
The inquiry centres on a record seizure of cannabis in Paris in 2015 - seven tonnes. Mr Thierry allegedly allowed a gang to import the drugs, so that their smuggling methods could be monitored.
He is quoted as saying justice officials knew about the operation.
The opening of a formal investigation can lead to charges, but for now Mr Thierry remains free.
He is suspected of "complicity in the storage, transportation and acquisition of drugs and complicity in the export of drugs by an organised gang", AFP news agency reports.