Stephan Turk, a Riviera jeweller is charged with murder after shooting a teenage robber in the back after being held at gunpoint.
The 67-year-old shot the 18-year-old in the back as he and another robber were driving off on a scooter with gems stolen from the shop in the centre of Nice.
Turk ran after the robbers and fired three shots at them as they sped away.
The thieves had kicked and punched the owner of La Turqoise, 23 rue de l'Angleterre, before forcing him to open his safe at gunpoint.
"Armed, aggressive thugs attacked me," Turk said in a statement to French television. "I regret what happened, I regret that he is dead. But it is him who decided to do what he did. It is normal that I would defend myself."
However, magistrates did not agree with his plea of self defence and after a court hearing, Turk was charged with murder. He was released from custody to stay at an agreed residence and to wear an electronic tag.
If convicted of voluntary homicide, the jeweller could spend the rest of his life in prison, and the story has triggered a national debate over what constitutes reasonable self-defence.
A Facebook page set up in Turk's support had attracted nearly a million "Likes".
French law allows for killers to escape conviction for murder if they can show they acted in "legitimate defence".
But the prosecutor who recommended Turk be charged does not believe that can be applied in this case as the jeweller's life did not appear to be in immediate danger when he fired an unlicensed 7.65 semi-automatic pistol.
The jeweller reportedly told the magistrates that he had fired his first two shots with the intention of demobilising the scooter and a third one in response to his victim threatening to shoot him with a rifle.
The dead youth, identified only by his first name, Anthony, had a string of convictions for theft, assault and driving offences.
"It is true that he did a lot of stupid things," his father told local newspaper Nice Matin. "He was a little delinquent, a scooter thief. But he had the face of a child and no child should have to die like that.
"I'm not defending what my son did, but, there, he has been shot like a pigeon."
Politicians have avoided commenting on the case, saying it is a matter for the courts. But it has been taken up by the far-right Front National.
"When people feel obliged to defend themselves with such dramatic consequences, it is a sign that they no longer have any confidence in the state or the forces of order," said FN leader Marine Le Pen in an AFP report.