The food the victims ordered was not touched.
The guests had been scheduled to check out on Monday.
They went from the hotel’s seventh floor to the fifth, where their bodies were found by housekeepers in the suite’s living room and bedroom.
Investigators say there is no evidence of a fight or a robbery, and the only wound found on one of the bodies was likely caused by a collapse.
In the bathroom, tea, energy drinks and honey were found, all in open containers, the police chief said.
It also appears that two of the victims tried to get to the hotel suite’s door, which was locked from the inside, but did not manage to reach it in time.
The victims’ luggage will now be searched as part of the investigation.
A spokesperson for the US State Department said they were “closely monitoring the situation”, and expressed their condolences to the families of the victims.
Matthew Miller added that Washington was “ready to provide assistance” to them.
The Grand Hyatt Erawan Bangkok is in a popular tourist spot. Some of the victims were visiting Thailand for the first time, while others had been before, a police officer who wished to remain anonymous said.
The prime minister said that he did not want this incident to affect Thailand’s image or have an impact on tourism – which is a key pillar of the Thai economy, but which has not fully recovered from the coronavirus pandemic.
The country has just expanded its visa-free entry scheme to 93 countries and territories in an effort to entice tourists back.