Leading article: The depths of this scandal are becoming clear

With each day that passes, the graver the News of the World phone-hacking scandal becomes. Earlier this month, the Labour MP Tom Watson told the House of Commons that he believed evidence existed that journalists employed on Rupert Murdoch's other UK newspaper titles had been involved in the practice (although this was denied by the media group). At the weekend we learned that the News of the World employed a private investigator, Jonathan Rees, who had been previously convicted for plotting to plant drugs in someone's car. And yesterday, Panorama broadcast claims that a journalist at the same paper paid a private investigator to hack into the computer of a former intelligence officer.

If true, Mr Watson's allegations would explode the argument from News International's management that illegal data acquisition was confined to just one "rogue" reporter at the News of the World. And that newspaper's employment of Rees makes it clear that its dubious news-gathering practices extended beyond the employment of the private investigator Glenn Mulcaire (convicted in 2007 for hacking the phones of aides to the Royal Family). The Panorama allegation is disturbing too. This was not the voicemail of some celebrity said to have been hacked, but the computer of someone who used to work for the security services. This could have compromised the details about the identities of informants, whose lives could have been put at risk as a result.

The unravelling of News International's original defence over hacking has also prompted something of a civil war within the criminal justice system. In recent days we have had the extraordinary sight of the Director of Public Prosecutions, Keir Starmer, writing a public letter to contradict an earlier missive by John Yates, the police officer formerly in charge of the hacking case, about the legal advice that was given by the DPP on evidence necessary to mount a prosecution. Each day we learn more about what took place – and who failed to act. We need to keep pressing until we have the full picture – no matter how embarrassing the process is for any of those involved.