
Tiwat Kasemchoke, 29, was taken in police custody Monday further investigation.
His victim, 45-year-old Astrid Al-Assaad Schachmer, was found dead on Sunday with bruises around her neck and her body topless.
"She had humiliated me. She often told other foreigners that I had fallen for her and tried to rape her several times, which is not true," Tiwat claimed, "It's she who wanted to be in a relationship".
Police summoned Tiwat for questioning Sunday's night because the German tourist was last seen alive in his company.
"I'd planned to kill her. So, I invited her to a party at a shop where I've been working," Tiwat said, "Then, I suggested that we walked to a beach together. That's where I punched and strangled her".
The German tourist had stayed on Koh Phangan since December 10 last year. The island is famous for its fullmoon parties. She also spent her fourmonth vacation on this island in 2007.
Koh Phangan Police Station superintendent Pol Colonel Charoon Uchuparp Monday said the tourist's body was already sent to the Royal Thai Police's Institute of Forensic Medicine in Bangkok for an autopsy that will determine the exact cause of her death.
"A medical examination by the Koh Phangan Hospital rules out the drowning as the cause of her death because her lungs were not flooded," Charoon said.