Nora Quoirin died from intestinal damage likely caused by prolonged hunger and stress, say Malaysian police.
There was no evidence she was kidnapped or raped, according to police who added that she died two to three days ago.
While the teen was missing her family said they believed she was abducted, but police insisted she had likely wandered off from a holiday cottage and got lost in the dense jungle.
The 15-year-old London teenager, who was born with the brain defect holoprosencephaly and was described by her family as "vulnerable", disappeared on Sunday, August 4.
Her body was discovered on Tuesday beside a small stream about 1.6 miles from the resort of Dusun, where she had been on holiday with her parents and two siblings.
Nora's devastated family, including Belfast mum Meabh, have said their "hearts are broken" and paid tribute to her as "the truest, most precious girl".
They made an emotional statement released through the trust, describing how the teenager, who lived in London and was the daughter of French-Irish parents, had "truly touched the world".
They said: "Nora is at the heart of our family. She is the truest, most precious girl and we love her infinitely.
"The cruelty of her being taken away is unbearable. Our hearts are broken."
They offered thanks to those involved in the search for the teenager, adding: "Nora has brought people together, especially from France, Ireland, Britain and Malaysia, united in their love and support for her and her family."
Hundreds of people were involved in the search operation and it was volunteer helpers who found the teenager's body.
Deputy police chief Mazlan Mansor told reporters at a press conference on Tuesday that the body "was not in any clothings" and that the probe was considering all possibilities, including the "angle of criminal investigation".
He said the body was found in an area that had previously been searched by rescuers.
Mr Searle appealed to people not to speculate about what happened to Nora, adding: "There will be a time for comment but that time is not now. Let the family grieve in peace."
During the 10-day search, the teenager's parents, Meabh and Sebastien Quoirin, thanked those looking for her, as fundraising pages set up by Nora's aunt and uncle collected more than £100,000 from well-wishers.
A book of condolence was opened on Wednesday at the city hall in Belfast, where Mrs Quoirin is from, with Lord Mayor of Belfast John Finucane the first to sign it.
He said the teenager's death was "heart-breaking", and praised the "clear and positive" show of solidarity from the Belfast public.
A special service was held on Tuesday at the south Belfast church where Nora was baptised. Her grandparents are parishioners.
The head teacher at Nora's school in Wandsworth, south-west London, paid tribute to her as "a delight to work with" and said her fellow pupils and others who knew her will be supported during a difficult time.
The Quoirins said Nora's condition meant she was not independent and had difficulty walking.
Describing her as a "very special person", they said she would not have gone anywhere alone.
Search crews looking for the teenager played her mother's voice in the dense Malaysian forest near where she disappeared.
Police had said Nora, who was travelling on an Irish passport, was believed to have climbed out of her resort room window.
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