Authorities investigating the death of Nora Quoirin in Malaysia should retain an "open mind" about the causes of her death, according to a former police officer who is advising her family.
Her unclothed body was discovered on Tuesday 1.6 miles away from the resort where she had been staying.
Nora's mother said there was no way Nora would have ventured out alone in the middle of the night.
The Quorin family lawyer Charles Morel told Ireland's RTE Radio 1 her parents still cannot understand how Nora would wander off by herself in the night - especially in such an unfamiliar place.
"We cannot exclude the criminal hypothesis... we have to wait for the complete result of the autopsy," said the lawyer.
He added: "[The family] are just now concerned about the truth, because they owe that to Nora."
Malaysian police say the teenager starved in the jungle after going missing during a family holiday, but Jim Gamble a former police officer advising the family - said a full account of her death has not been established.
Mr Gamble told the BBC's Breakfast programme: "We have some of the answers but not all of them.
"The family themselves have always had a question mark of whether there was any criminal activity involved and I think everyone should retain an open mind."
Malaysian police said Nora is likely to have spent a week in the jungle on her own.
The London teenager, who was born with the brain defect holoprosencephaly and was described by her family as "vulnerable", went missing from the resort of Dusun on Sunday August 4.
The 15-year-old had died between two and four days before her body was discovered, a post-mortem examination revealed.
A police chief said officers had uncovered no evidence of abduction or kidnapping "for the time being", but Mr Gamble insisted it could not be ruled out.
He said: "In the villa we do know that the downstairs window was broken so it couldn't have been locked by the family and could have been opened from outside.
"We know why Nora died, in simple terms from starvation, we know where she ended up, but we don't necessarily know how she got there.
"I am not trying to pour fuel on the speculative fire but all of those things need to be considered and we do need to keep an open mind as we move forward and as we look back to see what lessons can be learned."
Negeri Sembilan state police chief Mohamad Mat Yusop said on Thursday that the post-mortem examination had found no evidence that the teenager had been abducted or raped.
He said she had died between two and four days previously, from intestinal bleeding, most likely due to starvation and stress.
He added: "The cause of death was upper gastrointestinal bleeding due to a duodenal ulcer, complicated with perforation ... it could be due to a lack of food for a long period of time and due to prolonged stress."
He said there were some bruises on her legs but these would not have caused her death.
Further analysis is due on samples taken from her body, he said, adding that Nora's family are now free to take her back home.
Mr Gamble said the ordeal had been "the worst possible time" for Nora's family, adding: "I think the sooner the family are able to bring Nora home and begin the journey that their grieving process will take them on, the better."
The family need to be given "the time and the space to grieve with dignity" as they "bring this very, very special child home", he added.