Police investigators will ask for the post-mortem results of Lunlabelle, a young product presenter, and believe they can solve her mysterious death at a Bangkok condominium within 48 hours.

The family of the woman has pinned their hopes on a Line chat coversation that could shed light on her death.

Thitima, 25, also known as Lunlabelle or Belle, was found dead on a lobby sofa at a condo in Talat Phlu of Bangkok’s Thon Buri area in the early hours of Tuesday.

Footage from security cameras showed a young man carrying an apparently unconscious Thitima into the building around 6pm on Monday, and then taking her to a room on the sixth floor. After a few hours, the same man put her on the sofa in the lobby where she was later found dead.

A doctor’s preliminary examination suggested that she died of heart failure. Police earlier said hers was an unnatural death. An initial inspection found no traces of drugs or other substances in her body but it was not clear whether they had tested her for alcohol.

Citing a doctor who performed the autopsy, Thai media reported on Wednesday fluids were found in her vagina and there were traces of vaginal tear, but police have not confirmed it.

A TV talk show revealed the chat messages in a Line group of which Rachadech Wongtabutr, 24, or Nam Oun, the prime suspect in the case, was allegedly a member. The person believed to be him had chatted with the group before and possibly after Belle died.

During an interrogation, Mr Rachadech, who also works as product presenter or “pretty boy’’, told police on Wednesday that he and some friends, including Thitima, were drinking at a house where they were hired to work in Bang Bua Thong area of Nonthaburi. He said Thitima had several glasses of alcohol, became drunk and then unconscious. He then took her to his condo.

Thai media reported a set of Line chat screenshots showing a conversation of someone by the name "P.Mhee.Model" in the group while other members and some of their replies were pixellated.

The person posted a photo of an unconscious Thitima in a car at 4.48pm on Monday. Another member wrote: "Next time, have her drink only a little".  

Later, the person wrote at 5.55pm: "Her lips turn purple now. What should I do?" Then a reply: "What have you done?"

A photo of the woman in front of a lift was posted at 6.17pm with a message: "What should I do next?" Someone replied: "Carry her inside and clean her up."

At 7.27pm, a message read: "Her eyes are unfocused and her mouth is foaming. I thought RIP."

"At first I was told four bottles till drunk, so I gave her plenty."

Another message at 12.54pm read: "I couldn't wake her up." Then a reply: "Throw water at her. Do whatever it takes. It's no longer funny. Feel her pulse."

The person posted again: "I'm stumped. She's just drunk. Why so unconsious?"

After a few pixellated replies, the person posted at 1.41am: "So tired. Just carried her down to lobby."

At 1.48, the person wrote: "I'm back in the room. Belle's in lobby. She's still breathing."