A preliminary medical examination had found that Carl Davies died accidentally after a fall when his body was found on November 9th in Saint-Denis, the capital of the French overseas department.
But local prosecutor Richard Bometon on Friday opened an investigation for murder and rape over the death of Davies, who arrived on the island on November 7th on the container vessel Atlantic Trader, which he was protecting from piracy.
Davies, 33, was found dead on the morning of November 9th in a gutter on the outskirts of Saint-Denis after an evening spent in several bars along with two other British security agents who arrived with him on the same ship.
A first examination of his body concluded that a wound on his head indicated a fall of several metres. But an autopsy carried out on Thursday revealed a knife wound to the stomach, blows to the head and rape.
Examining magistrate Fabien Noailles called on the anti-crime brigade of the local police to lead an inquiry.
The British agent, an ex-soldier who served in Northern Ireland and Iraq, was seen for the last time on the night of November 7-8 in a Saint-Denis bar with the two other agents who, like him, were employed by a private British company.
Anglophile Eugene Evans, who spent the evening with the three men, told local newspapers "they were happy, looking for fun and paid for a lot of rounds".
When the bar closed, he said, Davies -- who had drunk a lot -- did not want to go to the casino with his friends but "wanted to meet women".
His family said he had been a Marine until 2005 before becoming a teacher at Sittingbourne in Kent, southeast England.
"But he needed action. He'd been away for two weeks when he was killed," his sister Kerrie told the local newspaper Le Journal de l'Ile de la Reunion.
Davies's disappearance was reported to the authorities on November 8th by shipping company CMACGM before the Atlantic Trader left in the evening for Mauritius.