Six people found dead after drinking cyanide from teacups in a luxury Bangkok hotel likely died in a murder-suicide caused by a dispute over money, police believe.

The six deceased were found by housekeepers at the five-star Grand Hyatt Erawan hotel in the heart of the Thai capital on Tuesday evening, by which point they had been dead for about 24 hours.

While the mysterious circumstances of their deaths initially fuelled rumours online, police now believe that one of the party carried out a money-driven murder-suicide.

According to Noppasin Punsawat, Bangkok’s deputy police chief, a husband and wife among the dead had invested about 10 million baht (£213,000) with two of the others to build a hospital in Japan. He said this may have been a motive.

“We are convinced that one of the six people found dead committed this crime,” Ms Noppasin said, without identifying the suspect.

The deceased have been named as four Vietnamese nationals: Thi Nguyen Phuong, 46, her husband Hong Pham Thanh, 49, Thi Nguyen Phuong Lan, 47, and Dinh Tran Phu, 37. The two others were Americans: Sherine Chong, 56, and Dang Hung Van, 55.

The alarm was raised after the group failed to check out of the hotel on Monday.

When staff entered the room, the luggage was packed and the six bodies weren’t together. Police said this suggested many of the group did not knowingly consume the poison and wait to die together.

Initial suspicions of cyanide emerged because the bodies showed traces of the deadly chemical and had purple lips – a key indicator of a lack of oxygen. Tests and the autopsy later confirmed this theory, with cyanide found on the bodies and in the teacups.

While photos of the aftermath of the scene show the white china teacups empty, the feast of fried rice and vegetables, which arrived at about 2pm the previous day, were untouched, still sealed in cling film.

According to the deputy police chief, Ms Chong was the only person in the room when the food was delivered. The waiter had offered to make the tea, but was refused. Authorities said Ms Chong “spoke very little and was visibly under stress”.

CCTV footage shows the rest of the group sporadically entering the room – which was locked from the inside – between 2.03pm and 2.17pm. When the scene was discovered at about 5pm the following day, there were no signs of a struggle.

The Thai authorities have been keen to reassure international visitors, in particular, that the Kingdom remains a safe place to visit. Last year, a shooting by a 14-year-old boy in a shopping mall in the capital spooked many visitors, especially those from China.

The country is heavily reliant on tourism, which accounts for about 20 per cent of all jobs and 12 per cent of the economy.

Srettha Thavisin, the Thai prime minister, visited the crime scene on Tuesday evening and on Wednesday said that the fatalities would likely not affect a conference with Sergei Tsivileva, the Russian energy minister, at the hotel later on Wednesday.

“This wasn’t an act of terrorism or a breach in security. Everything is fine,” Mr Thavisin said, adding that both the Vietnamese and US embassies had been contacted, and that American FBI officers were en route to assist in the investigation.