When Rebekah Brooks edited the News of the World, her time at the helm of Britain's biggest tabloid was characterised by one issue above all others.

The paper's aggressive campaigning for a "Sarah's Law", designed to protect Britain's young people from the clutches of predatory offenders, garnered international attention but provoked street riots as the public reacted to the tabloid's policy of "naming and shaming" paedophiles. The campaign, which went to the heart of every parent's greatest fear – the abduction of a child – was a response to the murder in 2000 of eight-year-old Sarah Payne by the serial offender Roy Whiting.

But when another young girl, Milly Dowler, 13, went missing less than two years later it seems that the response of the News of the World was to hack into the voicemail of her mobile phone, almost certainly after Milly had been murdered by the serial killer Levi Bellfield. Those actions, including the deleting of messages, gave false hope to Milly's parents that she was still alive and hampered the police's investigation. That news is almost certain to mark a colossal step change in the way that the phone-hacking scandal is regarded both by those in positions of power and influence – some of whom would still prefer the story to go away – and by the public. No longer can hacking be written off as merely a shortcut ruse for accruing celebrity gossip. This is way more serious.

The News of the World's readers, who until now have remained largely loyal despite the damning of the newspaper in certain other sections of the media, may no longer be so sympathetic to its peccadilloes. "Heinous" was the Dowler family's description of the News of the World's actions and the paper's readers will, no doubt, agree.

Until now, News International's damage limitation machine has managed to keep its flame-haired boss at arm's length from the hacking. It was admitted by way of a public apology this year that Ms Brooks, as the newly installed News International chief executive in 2009, could have done a better job in acknowledging the scale of the problem when the story started to blow up. But the hacking itself, it was argued, never happened on her watch.

Scotland Yard now says otherwise. Ms Brooks has largely managed to avoid speaking about hacking, avoiding successive requests from MPs for her to give evidence. She has some explaining to do now.