Police believe one of six Vietnamese people found dead at the Grand Hyatt Erawan Hotel in Bangkok on Tuesday evening poisoned the others and then committed suicide.

Police said on Wednesday morning that they had questioned the daughter of one of the victims and other witnesses.

“The case likely stems from a debt problem. There are no other possibilities. The culprit is among the six (dead) because they were the only people who entered the room. There were no others,” a police chief said.

Police had yet to identify the poison used, he said.

Six Vietnamese people were found dead in a room on the fifth floor of the Grand Hyatt Erawan Hotel in downtown Bangkok on Tuesday evening. 

A source said forensic police found a cyanide-like substance in used cups in room 502 where the bodies were found. 

A seventh Vietnamese person had booked the next door room. Police believe she was a younger sister of one of the six victims.

The woman had left the country on July 10, and was unlikely to have had anything to with the deaths. The killer was believed to have poisoned the five others before taking their own life, the source said.