On Sunday a German woman apparently drowned off the Seychelles island of Praslin, where she was holidaying with a friend.
Seychelles Police spokesman Jean Toussaint said the 72-year-old's body was found floating in the sea off Cote D'Or on the island's east side, just after 11am.
Mr Toussaint said the woman and her friend had arrived in the Seychelles on September 16 and were scheduled to return to Germany on October 1.
Investigators are awaiting the results of post mortem examinations on both the German and the South African.
Meanwhile, Sue and Mike Korkki, the mother and brother of the Korkki sisters, have flown to the Seychelles to try and get to the bottom of their tragic, unexpected deaths.
"It's all very surreal," another brother, Chris Korkki, who lives in Lakeville, Minnesota, said. "We don't know very much. Our family is still very much in shock. We're devastated."
Robin, 37, and Annie, 42, were found dead in their $2,600-a-night holiday villa at the Maia Luxury Resort and Spa at Anse Louis on Thursday, September 22.
According to the police, one of the hotel's butlers noticed the sisters had not opened up their villa entrance at 8.30am. When he called again at 11.00am, there was still no sign of either of them.
"The butler called in the hotel management for assistance before going into the room to find the two women unresponsive," a statement released by Seychelles Police said.
"A medical doctor was called in from the nearby Anse Boileau clinic who certified that both women were dead. No indication has been given as to the estimated time of death."
Police told the Seychelles News Agency that preliminary inquiries found "no sign of violence" on the bodies.
"There were no marks on them whatsoever," Seychelles Tourism Minister Alain St Ange told NBC News. "They had a good time in the day and then they went to their room."
Police spokesman Jean Toussaint said the sisters were last seen alive on Wednesday evening when "they were assisted to the villa by hotel staff, including the butler, because they were believed to be drunk since they were seen consuming alcohol from the hotel bars throughout the day".
Mr Toussaint told reporters at a press conference that medication had been found among the sisters' possessions. There were no obvious signs of physical violence in the room, he said.
"We are working on identifying the use and origin of some medication found in the room," he said, although he could not confirm whether police suspected it had anything to do with their deaths.
The sisters, who have been described by family as "inseparable" and "best friends", were born and raised in Minneapolis. Both had successful careers and were seasoned travellers. Robin worked as a commodities trader in Chicago while Annie was employed by JP Morgan Chase in Denver.
The women arrived in the Seychelles on September 15 and were having such a good time on the Indian Ocean paradise that they had decided to extend their stay by two days until September 24.
Chris Korkki said the family had learned nothing so far through official channels about his sisters' deaths. He said his mother Sue and brother Mike had travelled to the Seychelles to find answers and to make arrangements to bring his sisters' bodies back to the US.
"All I know is my mom and brother are working with local officials and the US Embassy," Mr Korkki told The Associated Press.
He said his sisters were adventurous women who wanted to experience life to the fullest.
"They were frequent travellers both domestically and internationally," he said.
"They were kind and generous and compassionate, and were wonderful people that had a positive impact on a huge number of people."
The family has set up a crowdfunding account to help pay for Sue and Mike Korkki's travel expenses and funeral arrangements for the sisters.
The Give Forward Campaign has raised more than US$27,000 in three days.
The sisters' bodies are currently being held at the Seychelles Hospital mortuary where post mortem examinations are expected to be carried out in the presence of a representative from the US Embassy in Mauritius.
"The police have no objection to this in the spirit of transparency," Mr Toussaint said.
The Seychelles has been plagued by a string of unexplained deaths involving foreign nationals in recent years, including six British and American sailors.