The bag belonged to Pichet Rabumpleung, who had stopped in the fast-food outlet for something to eat. His phone rang, he told police, and he walked outside the shop to take the call. When he came back, his bag was gone.
He asked KFC staff if they had seen anything, but they had not. He also asked tuk-tuk drivers if they had seen anyone carrying his bag. The answer from them, too, was negative.
He then asked the KFC staff to check footage from their security camera. He recorded the footage on his phone and then posted it on his Facebook account before informing police.
The video clearly shows a balding foreigner in shorts and a white singlet with the number 96 on the back, looking out of the window, and then around him.
He gets up from his seat, picking up a black baseball cap, his wallet and sunglasses, and then walks over to where Mr Pichet left his backpack.
He takes the bag and then calmly strolls out of the KFC.
Anyone knowing the foreigner is asked to contact police in Patong.
Original video here.