Murdered British backpackers Hannah Witheridge and David Miller may have been in a row in a bar with a local gangster who tried to chat her up.
But there were also fears the killer may already have fled the tiny Thai island of Koh Tao where the pair died.
Police are probing claims a drug called “ya ba” - pill available in certain bars on the island - may have been involved in the murder.
They are also trying to trace a mystery western woman seen on CCTV running along the main street in the early hours on the night of the murders.
Meanwhile DNA found on her body came from two unknown Asian men, tests revealed.