Judicial police late yesterday carried out the first searches at the Biotrial lab which had performed the trial on behalf of Portuguese pharmaceutical company Bial.
Yesterday they were joined by representatives of France's social affairs inspectorate general (IGAS) and the national drug safety agency (ANSM).
The probes are seeking to determine if the tragedy was caused by an error in the trial's procedures or in the substance tested, a new drug meant to treat mood disorders such as anxiety.
Pierre-Gilles Edan, head of the neurology department at the hospital in Rennes where the volunteers were taken, said Friday that aside from the man who was clinically dead, three others were suffering a "handicap that could be irreversible" and another also had neurological problems.
The sixth volunteer had no symptoms but was being monitored.
The head of Biotrial said today the lab was cooperating with the investigators.
The investigators and inspectors "are trying to understand.... What could have happened and how it could have resulted in such an a tragic situation," he said, adding that there was no news of any change to the condition of the hospitalised volunteers.
Representatives from Bial were also on site and taking part in the probes with "total transparency", according to Peaucelle.
France's national drug safety body confirmed it was the worst-ever incident to have taken place in a drugs trial in the country.
