Six people died from cyanide-laced drinks poisoned in a luxury hotel suite in Thailand, police said.
Police suspect one of the deceased was behind the poisoning because he was deeply in debt.
Six dead people were discovered by housekeepers at the Grand Hyatt Erawan Shrine hotel in the Thai capital Bangkok on Tuesday night.
Investigators believe they had been dead for 24 hours.
Authorities said two of the six had borrowed “tens of millions of baht” from another deceased person for investment purposes. Ten million baht is worth nearly $280,000 (£215,000).
The gruesome discovery of the body had earlier caused confusion and mystery, with local reports initially suggesting a shooting had taken place. Police later dismissed those reports.
There is now a clearer idea of what could happen.
At a news conference on Wednesday, Bangkok’s deputy police chief, Gen. Noppassin Poonsawat, said the group checked into separate hotels over the weekend and were assigned five rooms – four in seven. Floor, a room is on the fifth floor.
They were scheduled to check out on Monday but were unable to do so.
Two of the victims were U.S. citizens, 56-year-old Sherine Chong and 55-year-old Dang Hung Van.
The other four are Vietnamese citizens Thi Nguyen Phuong (46), her husband Hong Pham Thanh (49), Thi Nguyen Phuong Lan (47) and Dinh Tran Phu (37).
On Monday afternoon, all six gathered in a room on the fifth floor.
The group ordered food and tea, which were delivered to the room at around 14:00 local time (08:00 BST) and received by Ms Chong, the only person in the room at the time.
According to the deputy police chief, a waiter offered to make tea for the customer, but Ms. Zhang declined. The waitress recalled that she “spoke very little and was clearly under stress,” authorities said.
The waiter then left the room.
Others then started pouring into the room at various times between 14:03 and 14:17. It is believed that no one else entered the room other than the six people inside.
Police said there were no signs of a fight, robbery or forced entry.
They later found traces of cyanide in all six teacups.
Photos released by police showed several plates of untouched food left on the table in the room, some of which were covered with plastic wrap.
A seventh name was on the gang’s hotel reservation and police identified her as the sister of one of the victims. Police said she left Thailand last week for the Vietnamese coastal city of Da Nang and was not involved in the incident.
Relatives interviewed by police said Thi Nguyen Phuong and Hong Pham Thanh owned a road construction company and had provided Ms. Chong with funds to invest in a hospital construction project in Japan.
Police suspect that Mr. Tran, a makeup artist from Da Nang, was also “deceived” into investing.
Tran’s mother told the BBC he traveled to Thailand on Friday and called home on Sunday to say he had to extend his stay until Monday – the last time his family heard from him. She called him again on Monday, but no one answered.
Thai Prime Minister Sreeta Thawisin said the FBI was assisting Thai authorities in the investigation.
Additional reporting by Thuong Le for BBC Thai and BBC Vietnamese
