The show of solidarity is the latest in a series of demonstrations to support the 50-year-old doctor.
Dr Nicolas Bonnemaison, who worked in the accident and emergency department of Bayonne hospital (Pyrénées-Atlantiques), was taken into custody on Thursday after hospital staff brought in police to investigate the deaths of four patients.
The most recent was a 92-year-old woman who died on August 3rd.
He is being questioned over the “poisoning of vulnerable people”, an offence that can lead to imprisonment.
The case has sparked a new debate over assisted suicide in France.
A Facebook group already has over 10,000 followers, while an online petition in support of the doctor and addressed to the health minister had over 14,000 signatures by Tuesday morning.
The four patients were killed with a lethal injection of Hypnovel and Norcuron between April and August 2011. One of the patients who died was a woman of 92.
“This concerns extremely serious acts that are completely prohibited by law,” Marc Mariée, a prosecutor on the case, told a press conference. He confirmed that none of the families of the dead patients have made a formal complaint.
“My client has accepted the substance of the facts that have been put before him,” the doctor’s lawyer, Arnaud Dupin, told waiting journalists.
“He is a doctor who acted according to his conscience and his soul. He said he wanted to cut short the suffering of these people who were going to die in the minutes or hours to come and that they ought to be able to die with dignity.”
Dupin said that the families of the patients involved were “often” informed of the decisions taken by Dr Bonnemaison.
Assisted suicide is illegal in France but allowed in four European countries, Belgium, Luxembourg, the Netherlands and Switzerland.