They are working on several theories – suicide, accident or foul play.
Trevor Roberts, 74, was found floating face up in the river. He had been dead for about two hours.
There was a driving license in his pocket, 2,640 baht in cash, a house and car keys for a Mitsubishi.
He was wearing a watch and carrying an appointment card for a visit to the Krung Thep Phitsanulok Hospital.
There was no sign of his Mitsubishi car anywhere nearby.
Police contacted the younger sister of his wife called Phuangthong Nuanjan, 59, who said that Mr Roberts was a former language teacher at a college in the area and had been in town about ten years and was now retired.
He usually stayed home with his wife and her elder sister, but occasionally went to visit foreign friends in his car. He used to drink but had given up nearly a year ago, she said.
It is reported that she had been to visit the couple only a few days previously, when her sister had told her that the couple had been arguing lately. Mr Roberts had been complaining that he was in financial difficulty because his pension was less than before due to some British government changes in the way it was paid.
Apparently the wife did not accept this and suggested that her husband might be spending money on a woman on the side and this led to them arguing frequently.
Later Mrs Roberts told police that her husband had said two days ago that he wanted to die. She thought nothing of it at the time. On that particular day she had gone to town on business at 7:30 in the morning and on her return she was informed by her sister that her husband had been found floating in the river
Phitsanulok police are still concerned that they cannot find the victim’s car. They are as yet unsure as to whether he jumped in the river, had an accident involving his car or someone else was involved in his death.
Police have sent the body for a detailed autopsy, as the investigations continue.