The body of Tunchanok Donhomla was discovered in the coastal city of Pattaya in the early hours of Saturday. Police said the teenager had been reported missing at around 5pm on Friday.Authorities arrested 38-year-old Australian national Simon Peter Carman at Bangkok's Suvarnabhumi Airport on Saturday as he was allegedly preparing to leave the country.Investigators said CCTV footage showed Carman entering a condominium with Donhomla at around 3.34am on Thursday. Later that evening, cameras allegedly captured him leaving the building alone while carrying a large suitcase. Police said he then loaded the bag onto a motorbike and rode towards a railway line.The teenager's body was found about 15 minutes after Carman's arrest, according to Pattaya City Police.Carman has been charged with murder, concealing a body and taking a minor for sexual purposes. He has denied all the charges and claimed he acted in self-defence.Thai media reports said Carman told police that he had agreed to pay Donhomla 1,000 baht (about $30) for sexual services. He allegedly claimed the pair argued after returning to his apartment when he offered her only 500 baht ($15).Police also told the media that Carman claimed the teenager had "disappeared from the room" while he was asleep.In a video recorded while in custody, Carman addressed the victim's family, saying: "I feel bad for what happened to your daughter. It was out of my control.""I know you'll be very sad and upset, same as me," he said, before adding: "Please tell other girls just to be careful."