Photos of food in the room at the Grand Hyatt Erawan hotel where the murder-suicide occurred showed that some plates had their plastic wrap removed. However, there have not been any specific reports of any dishes containing cyanide.
Thai police still need more time to prove whom the cyanide belonged to, because of different evidence and a lot of people involved.
Earlier, autopsy results released on July 17 confirmed that the six people died of cyanide poisoning, a substance that causes acute asphyxia.
The six had been found dead in the locked room at the luxury hotel on Tuesday.
Police identified Vietnamese-American woman Sherine Chong, 56, as the suspected killer, and attributed the deaths to cyanide poisoning. Chong had also killed herself.
The other five were another American Dang Hung Van, 55, and Vietnamese nationals Nguyen Thi Phuong Lan, 47, Pham Hong Thanh, 49, Tran Dinh Phu, 37, and Nguyen Thi Phuong, 46.
The six had had a dispute over debts related to an investment, according to the police, who are still investigating how Chong obtained the cyanide and whether she had accomplices.
General Noppasin Poolsawat, deputy chief of the Bangkok police, told correspondents that the deceased had a dispute over a hospital construction project in Japan.