The six foreigners who were found dead at the Grand Hyatt Erawan Hotel in the Thai capital Bangkok on Tuesday likely died of cyanide poisoning, Thai police said on Wednesday.
The police also said one of the victims was the suspect in the case.
"We would like to confirm that one of the six dead caused this incident using cyanide," Noppasil Poonsawas, deputy commander of investigations at Bangkok's Metropolitan Police Bureau said at a press conference. "We are confident one of the six conducted the crime."
What did the police say?
The US Federal Bureau of Investigation assisted police with the investigation, they said. Two of the victims were US nationals.
"We found cyanide in the teacups, all six cups we found cyanide," Trirong Phiwpan, Commander of the Thai police evidence office, told a press conference.
"After [the] staff brought tea cups and two hot water bottles, milk and tea pots... one of the six introduced cyanide."
Through investigations with relatives, the police said they also found out the group had a dispute over debt related to an investment.
An autopsy report is due on Thursday, the police said.
What do we know about the deaths?
Thailand's Foreign Ministry said in a statement that the dead were reported to be two American citizens of Vietnamese origin and four Vietnamese nationals.
The Thai newspaper Matichon said that five bodies were found inside a room and one was found outside.
Bangkok police chief Thiti Sangsawang said that there were no signs of a struggle and that investigators suspected the six people had been poisoned.
Thai Prime Minister Srettha Thavisin went to the site of the incident in the evening but did not provide any additional information.
Police said that officers found the bodies of six deceased foreign nationals at the hotel after receiving a call from staff reporting that there had been deaths.
Thiti said that all six were supposed to check out on Tuesday and that their luggage had been packed.
He said that food had been ordered from room service but was left uneaten.
"What we can prove now is that they are not dead from suicide but from the killing of others," he had initially added, saying they were looking for a seventh person who was connected to the group.
Government fears damage to tourism
The Grand Hyatt Erawan is located in a popular tourist area known for luxury shopping and restaurants.
Srettha ordered a swift investigation to minimize damage to the tourism sector.
"The prime minister has ordered all agencies to urgently take action to avoid impact on tourism," the Thai government said in a statement.
More than 28 million foreign tourists visited Thailand last year, spending 1.2 trillion baht ($33.71 billion, €30.9 billion) in the country.
Thailand's government expects some 35 million foreign arrivals this year. It has provided longer visa stay periods and waivers for several nationalities.
