Initial autopsy results revealed traces of cyanide in the blood of six Vietnamese and American guests at the Grand Hyatt Erawan Bangkok, with one guest suspected of poisoning the others over a bad investment, Thai authorities said Wednesday.

The bodies were discovered Tuesday in the luxury hotel, located at a busy central intersection in the capital. The six guests were last seen alive Monday afternoon when food was delivered to their room.

Security footage showed them arriving one by one, and no one else entered or left the room, which was locked from the inside.

Hotel staff found untouched food and used teacups containing traces of cyanide, the Associated Press has reported.

Autopsies performed at Chulalongkorn Hospital confirmed the presence of cyanide in their blood, with no signs of blunt force trauma.

The victims were identified as two Vietnamese Americans and four Vietnamese nationals, aged 37 to 56. Bangkok police stated the case appeared personal and assured it would not impact tourist safety.

Written by B.C. Begley