The 13-year-old, who was also known as Milly, was identified using dental records after the discovery near Fleet in Hampshire, Detective Superintendent Alan Betts of Hampshire Police said.
Detective Chief Superintendent Craig Denholm, who led the investigation for Surrey Police, said: “Our worst fears have been confirmed and I can now tell you that the search for Milly has changed from a missing persons
inquiry into a murder investigation.”
Milly was last seen walking back from school to her home in Walton-on-Thames, Surrey on March 21.
Mr Betts told the press briefing that dental comparisons with remains found in Yateley Heath woods on Wednesday “are almost certainly those of missing Amanda. DNA tests will be carried out as soon as possible to confirm this”.
Det Chief Superintendent Denholm said: The news is very distressing to everyone involved in this inquiry. It’s much more distressing for Milly’s
parents, Bob and Sally Dowler, and her sister Gemma.
“Our thoughts and sympathies are with Milly’s family at this time. They are being kept fully informed of all developments.”
The remains were found next to a footpath in the woodland at Minley, near Fleet, Hampshire, on Wednesday at 2pm by a couple collecting mushrooms.
The couple did not contact the police until yesterday when they were accompanied by Surrey Police officers to the scene.
In interviews published before the latest developments, Amanda’s mother Sally, 43, said: “I think in the beginning my brain went into overload and I honestly felt in complete fear of losing my mind.
“I couldn’t cope because there was no answer. Right now if you asked me what do you think happened? I’d say she has been murdered.”
Just a week ago detectives released CCTV pictures which may have shown Amanda talking to the driver of a car moments before she vanished near Walton-on-Thames railway station.
The footage showed a figure standing next to a stationary dark saloon with a distinctive spoiler and apparently talking to someone inside.
The CCTV images were originally blocked out by sun glare but FBI experts at Quantico, Virginia, spent two months using hi-tech equipment to reveal them.
Police say they are “50% sure” the lone figure in the footage was Amanda, and described it as “massively significant”.