Nick Davies’ piece on what police now know about phone hacking and Milly Dowler is a brilliant example of how a journalist should never cling to one story of events, and also how timelines can be useful in checking stories.

“The new evidence … confirmed almost everything I had reported in July of this year. But one important element shifted: the police could no longer be sure exactly who had caused the particular deletions that led to that “false hope” moment.

“[T]wo pieces of new evidence have made the picture more complex. First, Surrey police have been able to establish the exact timing of the false-hope moment, at 7pm on the evening of Sunday 24 March 2002, three days after Milly was abducted. This was a surprise for the Dowlers who had always recalled that it happened two or three weeks after her disappearance. Original police records show that, understandably in the awful stress of events, their timeframe was distorted.

“Second, Scotland Yard concluded that Mulcaire was not tasked to intercept the girl’s messages until after that date. This was a surprise to Mulcaire who had felt very oppressed by the Dowler revelations and who, according to a close friend, was in tears after he heard the news.

“So who did delete the messages which gave false hope to the Dowlers? At first, one other fragment of new evidence appeared to provide the answer: records showed that Milly’s phone would automatically delete any message 72 hours after it had been listened to. The false-hope moment happened some 75 hours after she was abducted on Thursday afternoon, March 21. But this theory then collapsed, because the records also showed that she had not listened to her voicemail since the preceding day, so the 72-hour period had ended on the Saturday afternoon.”

The lesson is simple: when new evidence emerges, compare it against your own evidence and be prepared to acknowledge that facts may have changed. A witnesses’ perception of time can be affected by their emotional state at the time; potential answers can prove illusory; and the villain of the piece may have come onto the scene after the window of opportunity. Stories are not always as clear as they seem.