After receiving the call at 4am, Chalong police arrived to find the body of Nootsika Glaseuk from Ranong lying on the sidewalk surrounded by a large crowd of onlookers.
Ms Nootsika, who worked at the nearby Ginggaew Karaoke had been shot in the right side of her head, causing instantaneous death.
Questioning witnesses, officers learned that the victim had gone to the pub to eat and drink with friends. She left about 20 minutes later.
As she walked out a single shot was heard, fired from a pick-up truck driving east on Patak Rd (on the same side of the road as the pub) towards Chalong Circle.
Ms Nootsika collapsed on the ground.
It happened so fast that no one could give details of the truck, even its colour.
Police are working on the theory that Ms Nootsika was not specifically targeted, but was an innocent victim of the gunman who was shooting indiscriminately at the bar.
Investigators are examining security camera footage to try to identify the vehicle and the killer.