Following the discovery of six deceased individuals in a room at the Grand Hyatt Erawan in Bangkok on Tuesday, autopsy reports have revealed traces of a poisonous chemical in their systems.
Kornkiat Vongpaisarnsin, head of the forensic medicine department at Chulalongkorn University's medical school, conducted the autopsies and stated that cyanide was found in the blood of all six victims.
The six were last seen alive when room service delivered food to their room.
The staff saw one woman receive the food, and security video showed the rest arriving one by one shortly after.
There were no other visitors; no one was seen leaving, and the door was locked from the inside, according to the Associated Press.
When the maid happened upon their bodies, the food had not been touched; however, there were several used teacups on the nearby table with two thermos bottles.
Bangkok police chief Lt. Gen. Thiti Sangsawang previously identified the deceased as two Vietnamese Americans and four Vietnamese nationals and said they were three men and three women, ranging in age from 37 to 56.
Noppasin Punsawat, the Bangkok deputy police chief, believes the motive is personal after discovering the husband and wife among the dead had allegedly invested about 10 million baht ($278,000) with two of the others in the group.
The investment was for plans to build a hospital in Japan, and the meeting in Bangkok may have been to settle details.
Police stated one killed the rest but did not say which of the six was the suspect.
On Wednesday, Noppasin disclosed that a seventh person whose name was part of the hotel booking was a sibling of one of the six and left Thailand on July 10.
They believe this person had no involvement in the deaths.
"This wasn't an act of terrorism or a breach of security. Everything is fine," said Prime Minister Srettha Thavisin on the country's tourism sector.
U.S. State Department spokesperson Matthew Miller in Washington offered condolences to the families of the dead, and is closely monitoring the situation.
