Nora Quoirin's family still believe the teenager was taken despite a post-mortem saying she died from stress and starvation.
Nora's a 10-day search after she went missing on a family holiday.
The results of the post-mortem examination were revealed by police on Thursday and found she had starved and died of intestinal rupture.
But lawyer Charles Morel, acting on behalf of the 15-year-old's parents, said the couple have not ruled out pursuing a criminal probe.
Parents Sebastien, 47, and Meabh, 45, from Balham, south west London, are reportedly waiting for the results of DNA and toxicology tests before making a decision but said no avenue has been "excluded".
Speaking to Irish broadcaster RTE, Mr Morel said they "cannot understand how Nora could leave by herself" because of her disabilities.
He also urged "caution" over post-mortem results which showed Nora died of intestinal trauma, the Irish Mirror reports .
Mr Morel said: "We don't want the media to interpret the first result of the autopsy, excluding the criminal hypothesis. It's too early to say that.
"The family still finds it difficult to understand that she would have gone into the jungle on her own. They are concerned that she did not leave on her own.
"She was very shy, dependent on her mother and it's not in her temperament to go out in the night after a long trip in a place she doesn't know, in the jungle. They cannot understand how she could leave by herself.
"Even the place where she was found, two kilometres from the resort, it's very strange that she could go there by herself alone, so we cannot exclude the criminal hypothesis."
He added of the family: "They loved their daughter, she was an angel.
"But they are now concerned about the truth because they owe that to Nora, what happened, how did she die.
“In view of the importance of Malaysia’s image for tourism, the authorities may tend to favour the theory of a disappearance over the criminal hypothesis."
Police said on Thursday that there was no evidence the London schoolgirl was kidnapped or raped.
Detectives believe she left through the accommodation's ground-floor aluminium framed window before her father raised the alarm of her disappearance at 8am the following day.
It is thought she was alive in the dense jungle for six to seven days after vanishing and suffered a slow and agonising death as hundreds of trackers desperately tried to find her.
Nora, who was born with the brain defect holoprosencephaly and was described by her family as "vulnerable", went missing from the resort of Dusun on August 4.
Her unclothed body was discovered on Tuesday some 1.6 miles away and she had died between two and four days earlier, a post-mortem examination revealed.
A police chief told reporters that no evidence of abduction or kidnapping had been uncovered "for the time being".
Her remains were found by volunteer searchers beside a small stream in an area that rescuers had already looked at.
