A News of the World journalist told police they got Milly Dowler's mobile phone number and pin from other schoolchildren, a report revealed today.
Details of exchanges between police and the Sunday tabloid over the apparent hacking of the murdered schoolgirl's phone were released by Surrey Police.
An individual from the newspaper admitted in April 2002 that they had accessed Milly's voicemail, according to the force.
The information emerged with the publication of a letter from Surrey Police to the Commons Culture, Media and Sport Committee.
It describes frantic discussions over a story the NotW was planning to run wrongly, claiming that Milly had contacted a recruitment agency.
An unnamed representative from the tabloid is said to have played police a recording of a voicemail left by the recruitment agency.
The letter says that on April 13 2002, "the press officer spoke to (name redacted) and asked him why he was so convinced that the message on Milly's voicemail was not a hoax", the letter said.
"(Name redacted) response was that the NotW had got Milly's phone number and pin from schoolchildren."
The letter from Deputy Chief Constable Jerry Kirby was censored at the request of Scotland Yard officers investigating phone hacking.
A press officer from Surrey Police is said to have spoken to an individual from the NotW about the recruitment agency story - which initially suggested Milly may be alive - on April 20 2002.
By this time officers had established that the voicemail left for the murdered schoolgirl had actually been intended for someone else.
The NotW "played the Surrey Police press officer a recording of the message left by the recruitment agency on Milly's voicemail".
"The press officer stated that the name of the person seeking employment was 'Nana'," the document said.
"The press officer said that there were a number of people on the recruitment agency's books from Ghana, and that the call from the recruitment agency was intended for one of them.
"(Name redacted) responded by saying that what the Surrey Police press officer was saying was inconceivable. (They) said that there were other messages on Milly Dowler's phone (e.g. a message saying 'It is America, take it or leave it'."
The NotW also informed police that they knew of voicemails from "a tearful relative" and a "young boy".
Keith Vaz, chairman of the Commons Home Affairs Committee - which has also probed phone hacking - said: "The information provided by Surrey Police raises serious questions over what they knew about phone hacking and when.
"Had they acted in 2002 or had Sussex Police flagged this up in their review of Operation Ruby, it may have prevented the culture of hacking becoming endemic at News of the World.
"The Home Affairs Committee has also received a letter from Surrey Police with additional information to questions posed back in October 2011.
"We will be considering this information carefully and will look into investigating the reasons why Surrey Police did not follow up on this evidence."
The Metropolitan Police have indicated that, while reporters did access voicemails, they are unlikely to have been responsible for the deletions which gave the family false hope.
Instead the recordings may have been automatically removed by the phone company after being listened to.
The Surrey Police letter timetable published today - dated January 17 2012 - does not shed any further light on that issue.
It also dismisses the idea that the force was the source of the tabloid's stories, and said there was "no evidence" of any discussions about voicemail evidence after April 20 2002.
However, Mr Kirby stressed that the internal investigation is not yet complete.
"When and the extent to which Milly's mobile phone was unlawfully accessed (and whether any messages were deleted) are matters which form part of the Met Police Service's ongoing investigation," the letter added.
A statement issued on behalf of the Dowler family said: "The release of the Surrey Police statement is a further reminder of the relationship between that force and the News of the World.
"Current investigations are ongoing as to the propriety of that relationship.
"The report indicates that the police force were aware of a caller purporting to be Sally Dowler seeking information in 2002.
"No doubt there will be current investigations as to who that was as it was not Sally Dowler.
"The Surrey Police have not explained why they did not investigate that deception in 2002.
"No thought seems to have been given to the effect on the Dowler family. The family await the investigation by Lord Justice Leveson about the relationship between police forces and the Press.
"The Dowler family would be grateful if they could now be left alone."
Culture Committee chairman John Whittingdale told Sky News: "What (the letter) appears to tell is that several journalists at the News of the World were involved in hacking the voicemails left on Milly Dowler's phone.
"They did so in pursuit of a story rather than wanting to help the police with their inquiries.
"It appears as if they may have actually interfered or impeded the police in their investigations into what turned into a murder inquiry because they went on claiming they had evidence Milly Dowler was still alive."
The timeline raises fresh questions about the way detectives conducted the original investigation, and whether they could have been inadvertently responsible for triggering the deletion of voicemails.
Surrey Police first obtained an evidence Production Order and accessed Milly's voicemails on March 26, finding one message, according to the document.
But it was not until April 17 that the force secured a second Order and downloaded further messages, including that left by the recruitment agency.