Bob and Sally Dowler, Milly's parents

Credit: Stefan Rousseau/PA

The full story of what happened to murdered schoolgirl Milly Dowler's voicemail messages following her disappearance in March 2002 might never come out, the Metropolitan police admitted today.

In a statement read out to the Leveson inquiry, detective chief inspector John McDonald said "a definitive conclusion is not and may never be possible" because of incomplete call data from the mobile phone provider.

McDonald also revealed that mother Sally Dowler's "false hope" moment – when she was able to leave a message on her daughter's voicemail despite the mailbox previously being full – could have arisen because the mobile phone company automatically deleted voicemails after 72 hours.

He said a close analysis of call data suggested that "Mrs Dowler's false hope moment occurred on 24 March 2002", three days after the girl's voicemail filled up with messages following her disappearance.

Dowler's voicemail was put in a "preserved state" by the mobile phone company on 25 March to prevent further automatic deletions. A message was left the following day at 2:10pm, and when Surrey Police accessed the voicemail system two hours later, it was no longer showing as a new message, but appeared to have been read and saved.

When they came to download the messages on 17 April, the message was no longer present. A second message, left by the investigation team on 1 April, had also been erased.

McDonald told the inquiry that the police had also established that mobile provider One2One was in the process of moving voicemail platforms in the week following Dowler's disappearance – and that some archived messages from the old voicemail server were not picked up by Surrey Police as a result.

He said that while the Metropolitan police "cannot rule out that someone has illegally accessed" Dowler's voicemail, the call data from the mobile phone provider was incomplete and "we are unable to conclusively establish the accuracy of this theory".

He said: "It's currently the assessment of the inquiry team that no further clarity is likely to be provided. Ten years have lapsed. We will not be able to obtain a definitive explanation."

McDonald later added: "It is not possible to state with any certainty whether Milly's voicemails were or were not deleted. While a reasonable understanding of the events has been developed, reaching a definitive conclusion is not and may never be possible."

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