Gaia Pope had not suffered any injuries that would suggest she was murdered, detectives have said.
A post-mortem examination “has not identified any injuries to suggest any other person was involved in” the death of the teenager, who was found by specialist search teams in Swanage, Dorset, on Saturday 11 days after she went missing.
Two men aged 19 and 49 and a 71-year-old woman - all from Swanage and known to Gaia - were last week arrested on suspicion of murder but were released under investigation while enquiries continued.
The 19-year-old student was battling PTSD and suffered from epilepsy.
Dorset Police said they were “confident” the body is Gaia, which was found near the coastal path and the field where items of her clothing were located on Thursday.
Detective Superintendent Paul Kessell, of Dorset Police’s Major Crime Investigation Team, said: “The post-mortem examination has not identified any injuries to suggest any other person was involved in her death. The cause of death is undetermined pending toxicology.
“The coroner is involved in the oversight of these examinations but at this time this remains an investigation into an unexplained death.
“We would like to take this further opportunity to pass our thoughts to Gaia’s family who we continue to support and who ask for respect of their privacy at this incredibly stressful time.
“Once again I would like to pass our thanks to the public volunteers and partner organisations who have supported this inquiry throughout and have been material in locating Gaia.
“The area where the body was located is likely to remain cordoned off for some time while forensic examinations and searches are concluded.”
Gaia’s sister has described the teenager as “the absolute light of my life” following Saturday’s discovery.
Clara Pope said her sister was “so beautiful, so emotionally wise and intelligent and so passionate and artistic and creative and understanding”.
Hundreds of volunteers have been helping in the search effort in a bid to find the teenager.
Gaia had not been seen since about 4pm on November 7 in Manor Gardens, Swanage.
An hour earlier she was captured on CCTV buying an ice cream inside St Michael’s Garage in the town, having been driven there by a relative.
She was said to be wearing a red checked shirt with white buttons, grey and white woven leggings and white trainers. The black jacket she had on was recovered from an address in Manor Gardens.