Traces of cyanide have been found in the blood of six people found dead in a central Bangkok luxury hotel, forensic experts have said.

The bodies were found in the Grand Hyatt Erawan Bangkok.

Officers said that upon checking hotel records and security footage, there were no other visitors to the room apart from the six people who were found dead.

Doctors who performed post-mortem examinations on the six guests confirmed that they had traces of cyanide in their blood.

Dr Kornkiat Vongpaisarnsin, head of the forensic medicine department at Chulalongkorn University’s medical school, said at a news conference that a CAT scan showed no signs of blunt force trauma on the dead, reinforcing the hypothesis that they had been poisoned.

Earlier, Lt Gen Trairong Piwpan, chief of the Thai police force’s forensic division, said there were traces of cyanide in cups and containers that police found in the room.

Bangkok police chief Lt Gen Thiti Sangsawang identified the dead as two Vietnamese Americans and four Vietnamese nationals, and said there were three men and three women.

Their ages ranged from 37 to 56, according to Noppasin Punsawat, Bangkok deputy police chief. He said the case appeared to be personal and would not impact upon the safety of tourists.

The Vietnamese and US embassies have been contacted over the deaths, and the American FBI is en route, said Prime Minister Srettha Thavisin.

A husband and wife among the dead had invested money with two of the other victims, suggesting that money could be a motive, said the police chief.

The investment was meant to build a hospital in Japan and the group might have been meeting to settle the matter.

The six had last been seen alive when food was delivered to the room on Monday afternoon. The staff saw one woman who received the food, and security footage showed the rest arriving one by one to the room shortly after.

No-one was seen leaving and the door was locked from the inside. A hotel maid found the bodies on Tuesday afternoon when they failed to check out of the room.

Officers said a seventh person whose name was part of the hotel booking was identified by police as a sibling of one of the six victims, who left the country on July 10. Police believe the seventh person had no involvement in the deaths.

When asked if the news would affect a conference with Russian energy minister Sergei Tsivilev at the hotel later on Wednesday, Mr Srettha said it was unlikely. “This wasn’t an act of terrorism or a breach in security, everything is fine.”

Mr Trairong said a mass suicide was also unlikely because some of the victims had arranged future things for their trip, such as guides and drivers.

He added that the bodies were not grouped in the same place – some were in the bedroom, some in the living room – suggesting that they did not knowingly consume poison and wait for their death together.

In 2023, the country was rocked by reports of a serial killer who poisoned 15 people with cyanide over a span of years.

Sararat Rangsiwuthaporn, or “Am Cyanide” as she would later be called, killed at least 14 people who she owed money to and became the country’s first female serial killer. One person survived.