The six people who died in a luxury hotel suite in Bangkok are suspected to have been poisoned by drinks spiked with cyanide, Thai police said on Jul. 17.

Police suspect that one of the six had poisoned the entire group over a debt issue, Thai media reported.

The discovery

Bodies of the six were first discovered in a hotel room on the fifth floor of the Grand Hyatt Erawan hotel in Bangkok, on Jul. 16.

The door was ajar and the guests' luggages had been packed.

They had been expected to check out of the hotel the same day.

Two of the dead were identified as Vietnamese Americans and the other four were Vietnamese nationals, AP News reported.

They had last been seen alive when food was delivered to the room on the afternoon of Jul. 15.

Cyanide poisoning suspected over debt issue

Police suspect the six died of cyanide poisoning as traces of a "cyanide-like substance" were later found in the drinking glasses and a teapot in the room, Reuters reported.

Autopsy results are expected to be out on Jul. 18.

Thailand's Metropolitan Police Bureau investigation chief Theeradet Thumsuthee also said on Jul. 17 that the case "likely stems from a debt problem", Bangkok Post reported.

He added that police suspect one of the six deceased poisoned the rest.

“There are no other possibilities. The culprit is among the six (dead) because they were the only people who entered the room. There were no others,” Theeradet added.

Mass suicide 'unlikely'

Trairong Piwpan, chief of the Thai police's forensic division, also said that the possibility of a mass suicide was "unlikely", according to AP News.

He pointed out that some of the victims had made future arrangements for their trip, such as guides and drivers.

Trairong added that police did not find the bodies grouped in the same room, which suggested that they did not poison themselves and wait for death together.

U.S. citizen, 56, suspected to have poisoned group

More details were disclosed in a press conference on Jul. 17.

According to BBC, Bangkok deputy police chief Noppassin Poonsawat said the group checked into the hotel separately and occupied five rooms - four on the seventh floor, and one on the fifth.

The group ordered food and tea, which was delivered to the fifth-floor room at around 2pm on Jul. 15.

It was received by one of the six, Sherine Chong, a 56-year-old U.S. citizen.

According to Noppassin, a waiter offered to make tea for the guests but Chong refused this.

The waiter recalled that she “spoke very little and was visibly under stress”, Noppassin added.

According to Bloomberg, the U.S. law enforcement agency, the Federal Bureau of Investigation (FBI) has joined the probe by the Thai authorities.

Relatives of two in the group, a Vietnamese couple named Thi Nguyen Phuong and Hong Pham Thanh, told police that they owned a road construction business and had given money to Chong to invest in a building project in Japan.

Police also suspect that another of the deceased, Dinh, a make-up artist based in Da Nang, had been “duped" into making an investment.

Top image from Khaosod English