Thai police have announced that the deaths of six Vietnamese people in a room at a hotel in Bangkok on Tuesday were related to debt conflicts, and one of them had poisoned the others with cyanide before committing suicide.

Major General Theeradet Thumsuthee made the announcement at Lumpini police station on Wednesday morning, according to the Bangkok Post.

These six Vietnamese, two of whom also carried U.S. passports, were found dead in a room at Grand Hyatt Erawan Hotel in Bangkok on Tuesday.

Four of the victims were Vietnamese, namely Nguyen Thi Phuong Lan, 47 years old, Pham Hong Thanh, 49, Tran Dinh Phu, 37, and Nguyen Thi Phuong, 46.

The other two held U.S. nationality as well, including Chong Sherine, 56, and Dang Hung Van, 55.

Among these six people, Sherine, a woman, had poisoned the others before she committed suicide by possibly drinking a toxic substance, Thailand’s Khaosod newspaper reported.  

Police questioned the daughter of one of the victims and other witnesses, and their bank accounts became useful for the investigation, Major General Theeradet said.

The incident could have stemmed from debt issues and there is no other possibility, he stated. 

The official affirmed that the culprit was among the six people because they were the only individuals who entered and stayed in the room.

One more person, the seventh Vietnamese in the case, had booked the room next to the one where the dead bodies were found, and police believe that this person is the sister of one of the six victims. 

This woman left Thailand on July 10 and appeared to have nothing to do with the poisoning, police said.

On Tuesday evening, initial investigation results showed that the victims' room was locked from the inside and there was no sign of anyone breaking into the room to kill them.

After moving their bodies to a nearby hospital, Thai police also transferred the luggage of the six victims from the hotel to the Lumpini Ward Police headquarters for examination.

Reuters quoted Thai police as saying at a press conference on Tuesday morning that cyanide poisoning could be the cause of death of the six victims.

Police added that cyanide was found in the used drinking glasses and water bottles in room 502, where the bodies had been discovered.

According to police officers, after the hotel staff brought the glasses, two bottles of hot water, milk, and a pot of tea into the room, one of the six individuals added cyanide to the drinks. The autopsy results are expected to be available the next day.

Thanh and Phuong, among the victims, were husband and wife and owned a road and bridge building company in Vietnam, Krungthep Turakij newspaper quoted an initial report from the investigation team as saying, noting that they had interrogated the daughter of the couple.

The daughter said her parents came to Thailand to negotiate about an amount worth millions of Thai baht (1 million baht = US$27,875) they had lent to others. 

This detail led police to believe that the couple was poisoned due to the debt negotiation failure.

Khaosod newspaper also cited police as reporting that Thanh and Phuong had repeatedly asked Sherine to repay his debt, but were unsuccessful. They were then advised to travel to Japan for debt settlement.

Failing to get a visa to Japan, the couple went to Thailand to meet Sherine.

In an announcement on Wednesday morning, Thai Prime Minister Srettha Thavisin confirmed that a working group from the U.S. Federal Bureau of Investigation (FBI) will be coming to Thailand to assist with the investigation, particularly regarding the two deceased victims who held U.S. nationality.

PM Srettha said he met Vietnamese Ambassador to Thailand Pham Viet Hung at the hotel on Tuesday and confirmed to the diplomat that he had directed local authorities to launch a comprehensive probe into the case to announce the results soon.

Earlier, the hotel reported that a group of seven people had reserved five rooms. Eventually, five of them checked in, with four rooms on the seventh floor and one room, numbered 502, on the fifth floor. Their check-ins were recorded at different times on July 13 and 14.

At noon on Monday, the guests of the four rooms on the 7th floor returned to their rooms and all their luggage was brought down to room 502 on the fifth floor.

On Tuesday afternoon, hotel staff came to the room to conduct an inspection after the victims failed to check out by noon as scheduled.

As the room door was locked from inside, the staff had to enter the room through the back door and discovered the six bodies.

The staff called police immediately and at around 5:00 pm, police officers and a forensic team arrived at the scene.

Four of the six bodies were discovered in the living area of the room, while the other two were found in the bedroom.

According to Matichon newspaper, the hotel's camera footage revealed that the six individuals had earlier brought luggage into the room, and no one left the room until the deaths were discovered.

Investigators said the victims ordered six food portions from the hotel at 1:00 pm on Tuesday and there were no signs that they had touched the foods. 

However, police officers found five cups and a glass containing drinks in the room and said that some of those drinks could have been consumed by the victims.

All the suspicious things in the room have been collected by police officers for their investigation.

On Wednesday afternoon, addressing reporters' questions about the mass deaths, Vietnamese Ministry of Foreign Affairs spokesperson Pham Thu Hang stated that the Vietnamese Embassy in Thailand is closely coordinating with local authorities to verify and clarify the circumstances surrounding the victims' deaths, and to implement citizen protection measures.

The embassy is working with Vietnam’s Ministry of Public Security to check the identities of the victims. 

“We would like to send our deep condolences to the families of the victims and hope that they will soon recover from this great loss,” Hang said.

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