Thawatchai Sae Sim, 32, a rescue worker, was apprehended by police after the body of the woman was found near a canal in Bang Phli. She was later identified as Chananchita Suasew, 29, a public relations employee at a property development firm in Thong Lor.
The police said Mr Thawatchai denied killing the woman but confessed that he had tried to rape and rob her.
He said he attempted to rape her when she was unconscious, but was unsuccessful because she regained consciousness, so he ran away. The man said he later learned that the women had died.
Police took Mr Thawatchai to re-enact his crime at the canal in Bang Phli district on Wednesday afternoon.
He has been charged with attempted rape and robbery. Police said they will await the forensic results before deciding whether to press more charges. Mr Thawatchai also tested positive for using an illegal drug, and will be charged accordingly.
The alleged attack occurred late Monday morning. The department store called the rescue service for help after the woman lost consciousness at a food outlet inside the store. She was to be taken to Ramkhamhaeng hospital.
Mr Thatwatchai helped put her in the front-seat of a pick-up truck adapted for use as a rescue vehicle, and also helped carry her bag.
The department store contacted the woman’s family and her boyfriend went to meet her at Ramkhamhaeng hospital, but could not find her. The man then reported her missing at Hua Mark police station.
Late Monday afternoon, Bang Phli police station received a report of a dead woman in a canal. Police sent to the scene found Chananchita face down in the canal.
Sithichai Koyani, 34, who reported the incident, told the police that he and his wife were on a motorbike when the women ran out from the roadside and asked for help saying she had been raped. They picked her up but after a short ride, she asked to get off and ran back toward the spot where they picked her up.
They were worried about the woman so went back to look for her with another passer-by. They were unable to find her at first. After a further search they found her face down in the canal.
The story was reported on social networks, which is how the victim's boyfriend learned of her death.
Chananchita’s boyfriend and her mother went to Bang Phli police station and confirmed her identity on Tuesday.