Cyanide has been found in the blood of all six people who died in a luxury hotel suite in Bangkok, say doctors after examining their bodies.
Based on the initial post-mortem examination, they say there is “no other cause” that would explain their deaths “except for cyanide”.
But further tests are being carried out to determine the “intensity” of the deadly chemical and to rule out any other toxins.
Forensic investigators had earlier found traces of cyanide on the teacups used by the victims, all of whom are of Vietnamese origin including two with dual US citizenship. Police suspect that one of the dead was behind the poisoning and was driven by crushing debt – but have not said who.
The victims’ lips and nails had turned dark purple indicating a lack of oxygen, while their internal organs turned “blood red”, which is another sign of cyanide poisoning, said Professor Kornkiat Vongpaisarnsin of the Department of Forensic Medicine at Chulalongkorn University.
Doctor Chanchai Sittipunt, the dean of the Faculty of Medicine, said they still needed to find out how much cyanide was in the blood of the deceased.
“But from what we have detected – from observation, from internal organ check, from finding cyanide in the blood during the screening test – there is no other cause that would be the factor that would cause their deaths, except for cyanide,” he told reporters.
The deceased were found by housekeepers at the Grand Hyatt Erawan hotel in the Thai capital late on Tuesday.
Investigators believe they had been dead for between 12 and 24 hours by then.
The mystery around the shocking discovery made international headlines.
Thailand’s Prime Minister Srettha Thavisin ordered an urgent investigation into the case, stressing that the deaths were the result of a “private matter”, and there was no suggestion of public danger.
Police have since begun to piece together what might have happened.
Two of the six victims had loaned “tens of millions of Thai baht” to another of the deceased for investment purposes, authorities said. Ten million baht is worth nearly $280,000 (£215,000).
Earlier on Wednesday, Deputy Bangkok police chief Gen Noppassin Poonsawat told a press conference the group checked into the hotel separately over the weekend and were assigned five rooms – four on the seventh floor, and one on the fifth.
They had been scheduled to check out on Monday but failed to do so.
Four of the victims are Vietnamese nationals Thi Nguyen Phuong, 46, her husband Hong Pham Thanh, 49, Thi Nguyen Phuong Lan, 47, and Dinh Tran Phu, 37.
The other two are American citizens Sherine Chong, 56, and Dang Hung Van, 55.
The US state department has offered its condolences and said it is “closely monitoring” the situation. The US Federal Bureau of Investigation is assisting Thai authorities in the investigation, Mr Srettha said.
