When a waiter delivered food and tea to Sherine Chong’s hotel room, he could see she was stressed.

The walls of the luxury room in Bangkok’s Grand Hyatt Erawan were closing in on the 56-year-old, who was under pressure, in huge debt and facing legal action over a business dispute.

She had been lent hundreds of thousands of dollars to invest in a project to build a hospital in Japan, but there’d been no progress and the investors wanted their money back.

With the parties scheduled to meet in court in two weeks, she’d invited them to Bangkok for out-of-court negotiations.

On Monday, the group gathered in Ms Chong’s room at the swanky hotel in central Bangkok for lunch and tea.

When the waiter offered to brew the tea, Ms Chong refused and said she would prepare it herself.

Just over 24 hours later, all six people were found dead in that hotel room, their lips and fingernails black – the telltale signs of cyanide poisoning.

Bowls of tom yum soup and fried rice were untouched, but all six tea cups had traces of the deadly poison.

Police said they believed one of the six had killed the others before taking their own life, but did not name a suspect.

However, they added Ms Chong was the only person in her room when the food and tea were delivered.

An investment gone bad

Police said two members of the group – married couple Nguyen Thi Phong and Pham Thanh Hong — had given Ms Chong more than $400,000 for the hospital project.

According to the BBC, they also suspected her personal make-up artist for the trip, 37-year-old Tran Dinh Phu, had been duped into putting in some of his own money.

When the hospital project stalled and the couple took legal action, Ms Chong asked to meet.

The group had initially planned to go to Japan, but some members had visa issues so they decided on Bangkok instead.

Some members tacked on tours and had other travel planned for when business was out of the way.

After the five other members of the group checked out at noon on Monday, Ms Chong invited them to her room for a final round of talks over room-service food and tea.

CCTV showed all six members of the group gathering outside the room and then entering — the last time they were seen alive.

The following day, when a maid went in to check the room after Ms Chong failed to check out, she found the three men and three women dead on the floor.

Four were found in the living room, and two in the bedroom.

One of the men had been apparently trying to reach the door but collapsed before he was able to.

The dead – ranging in age from 37 to 56 – were all of Vietnamese descent, with two of them United States citizens.

Thai Police have been coordinating with the embassies of Vietnam and the United States to solve the case, and officials from the Federal Bureau of Investigation have travelled to Bangkok to assist.

Vietnam’s foreign ministry said its embassy in Thailand was coordinating closely with local authorities.

“We hope that the victims’ families soon overcome this great loss,” spokesman Pham Thu Hang said in a statement.

Questions over how killer accessed cyanide

Autopsy reports from Bangkok’s Chulalongkorn Hospital quickly confirmed what police had already suspected – all six bodies contained traces of cyanide.

Initial results found signs of asphyxiation and unusual congestion and colouring of the blood – typical of cyanide victims.

Professor Winai Wananukul from the Ramathibodi Poison Center said the fast-acting poison cuts off the supply of oxygen.

“It has effect of making cells in the body unable to use oxygen, so it has the same effect as when the body is deprived of oxygen,” he told the ABC.

“Cyanide acts very fast in a few minutes of ingesting by eating or inhaling.”

He said it was unclear how the cyanide had come into the alleged killer’s possession and whether it was procured in Thailand or brought into the country from Vietnam.

“It is already a controlled substance, but how much we can enforce that is a different issue,” he said.