Cyanide likely what killed 6, including 2 U.S. citizens, in luxury Thailand hotel room

July 17 (UPI) -- The six bodies, including those of two U.S. citizens, found Tuesday in a Thailand hotel room died after drinking from cups laced with cyanide in an incident possibly tied to a financial dispute or bad investment, officials say.

Three women and three men, four Vietnamese citizens and two Vietnamese-Americans, were discovered Tuesday in downtown Bangkok, Thailand's capital city, in a possible murder by poisoning on the fifth floor of the five-star Grand Hyatt Erwan Hotel after failing to check-out by more than 24 hours.

The four Vietnamese nationals included a married couple: Thi Nguyen Phuong, 46, and her husband, Hong Pham Thanh, 49. It also included Thi Nguyen Phuong Lan, 47, and Dinh Tran Phu, 37. The other two are American citizens Sherine Chong, 56, and Dang Hung Van, 55.

"Cyanide was found in the liquid inside the teapot, in all six coffee cups," Chief of the Police Forensic Office Trairong Phiewphan said Wednesday during a news conference.

Authorities first said they were looking for a seventh missing person part of the hotel booking as a possible suspect, only to dismiss that theory Wednesday when police identified the individual as a victims' younger sister who had left Thailand for Vietnam, indicating how police believe the person who poisoned the group very likely was among one of the dead.

Four of the bodies were located in the hotel room's living room and two in a bedroom. The room was found locked from the inside after the bodies were discovered, along with their packed bags in a discovery made by a hotel maid after the victims failed to check out Monday as scheduled.

Investigators say the bodies could have been dead for at least 12 to 24 hours as a preliminary examination of the scene by officials pointed to a poisoning. Cups of coffee and tea with traces of white powder, now identified as cyanide, were found in the room and untouched food previously brought by room service.

The incident took place in busy downtown Bangkok next to the Erawan shrine -- a place of significance for the Buddhist, Hindu and Sikh communities -- and site of a targeted 2015 bombing which killed at least 20 people.

All of the victims arrived on July 13 and the next day, and were staying in five different rooms, officials said Tuesday, and it was believed at the time some were family relations as they shared the same last name.

Police are leaning toward murder, not suicide, but the motive is still not fully clear as relatives point to a bad financial investment as a possible reason for the grisly scene. Police say the party on Monday all had moved into the same suite, having room service delivered around 2 p.m. local time but no person left or entered the suite after 2:17 p.m. local time.

The six victims' lips and nails turned dark purple which indicated lack of oxygen while their internal organs turned "blood red," another sign of cyanide poisoning, a Chulalongkorn University professor told BBC .

Thai police said their investigation found that Chong had allegedly ordered the food and drinks from room service and "looked under stress" when hotel staff arrived to deliver the items. She was the only person seen in the room when room service got there.

"But from what we have detected -- from observation, from internal organ check, from finding cyanide in the blood during the screening test," Dr. Chanchai Sittipunt, Chulalongkorn's dean of the Faculty of Medicine, told reporters.

"There is no other cause that would be the factor that would cause their deaths, except for cyanide," he said.

Relatives told police Thi Nguyen Phuong and Hong Pham Thanh owned a road construction business and allegedly gave money to Chong to invest in a Japanese hospital building project.

Chong allegedly hired Tran as her personal make-up artist for the trip while Tran's father told reporters his son was hired last week by a Vietnamese woman to travel to Thailand. Thai police suspect that Tran, a make-up artist based in Da Nang in Vietnam, had also been "duped" into investing.

The State Department said Tuesday it was "aware of reports of the deaths of two U.S. citizens in Bangkok" as the investigation keeps on.

"Whenever a U.S. citizen dies in a foreign country, local authorities are responsible for determining the cause of death," said State Department spokesperson Matthew Miller . "We do reach out to local authorities often to communicate with them when it involves the death of a US citizen and we will certainly be doing so here."