The owner of the house, Stein Håvard Dokset, 50, a retired man from Norway, denied all knowledge of the half-corpse, which was found wrapped in a garbage bag and stuffed into a municipal garbage bin in a locked bathroom on the ground floor.
He told police that he had not been in that bathroom for at least six months, and was mystified as to how it got there.
The body was in such an advanced state of decay that police could not immediately say whether the body parts came from a man or a woman. Forensic scientists in Surat Thani will try to establish its gender and take DNA samples in hope of identifying the dead person.
Mr Dokset was charged with possession of a gun without a permit. He is being held in custody until DNA results are received, expected to be this afternoon.
Police suspect the remains may be those of Rungnapa Rachsombat, also known as Rungnapa Suktong, 33, who disappeared three years ago. She had lived with Mr Dokset for about six years but broke up with him and moved in with a local policeman whom she had secretly married a year before.
The marriage fell apart and the two separated. Two months after leaving Mr Dokset, she disappeared.
Her family filed a missing person report with Kathu Police in July 2009.
Although the body has yet to be identified, police found a 9mm pistol registered to Ms Rungnapa in Mr Dokset’s study, along with two magazines and 58 bullets, and a handbag belonging to her.
The handbag contained her mobile phone, a watch, a purse, her ID card, her driving licence and credit cards.
Mr Dokset told police that he had no idea how the body into his house. “I don’t know who put this garbage in my house. I didn’t notice any smell. My garbage is outside. The one inside the bathroom is not mine.
“If I killed her I wouldn’t keep her in the garbage, in my bathroom, in my house for years.”
Police are now trying to discover what happened to the upper part of the body.
It is understood that Mr Dokset studied medicine when a young man, but did not graduate.
The case has grim echoes of the still unsolved 1947 Black Dahlia murder in Los Angeles. The victim in that case, Elizabeth Short, was found cut in half. Her murderer has never been identified.