Leading article: A crucial week for Leveson

By the time part one of the Leveson Inquiry into press ethics finished taking evidence into phone hacking a few weeks ago, most people who had followed it felt somewhat wiser than they had been on the culture of wrongdoing that appeared to have flourished at one point in Rupert Murdoch's media empire.

That is as it should be. People have a right to know to what degree contempt for the law had become routine in some sections of the media. But the bigger question is why the police tacitly allowed or were actively complicit in these unlawful practices over many years. This is why the second part of the inquiry, Module 2, into the relationship between the press and the police, which starts today, is so important.

The list of names appearing this week starts with Sue Akers, current head of Scotland Yard's investigation into phone hacking, who takes the stand today, and Philip Williams, who led the original investigation, who will appear two days later. Thursday will be an especially important day, when the former Met Commissioner, Sir Paul Stephenson, and the former Assistant Commissioner, John Yates, both of whom resigned last July following criticism of their handling of the original inquiry, appear.

We deserve some more satisfactory answers about the police's conduct than the ones we have been presented with so far, starting with why Surrey Police knew about but did not investigate the News of the World for hacking into the phone of the murdered teenager Milly Dowler almost a decade ago. From then on, until the Met's failure in 2009 to reopen the investigation, which Mr Yates last year admitted was a "pretty crap" decision, the trail of errors and cover-ups – we still don't know enough about the motives behind these actions – continued.

There are two more modules to go in the inquiry, but when the report arrives, the hope is that it brings some clarity to the business of whether it was incompetence or something much worse that lay behind years of repeated failures to get to the bottom of the phone-hacking saga. If the close links that existed between the Yard and News International are not properly explained, we should all feel short-changed.