BANGKOK (AP) Initial autopsy results showed traces of cyanide in the blood of six Vietnamese and American guests at a luxury hotel in central Bangkok and one of them is believed to have poisoned the others over a bad investment, Thai authorities said Wednesday.

The bodies were found Tuesday in the Grand Hyatt Erawan Bangkok, a landmark at a central intersection in the capital busy with malls, government buildings and public transit.

The six had last been seen alive when food was delivered to the room Monday afternoon. 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. A maid found them Tuesday afternoon when they failed to check out of the room.

Upon entering the room, hotel staff found that food ordered from the previous day was left untouched, with some servings of fried rice still under plastic wrap. While the food was untouched, several used teacups were on a nearby table, next to two thermos bottles.