Ian Burrell: A disturbing day for News International's heavyweights

Rupert Murdoch's News International, publisher of the News of the World, yesterday issued a statement about its pro-activity in the current police investigation. "News International has consistently reiterated that it will not tolerate wrongdoing and is committed to acting on evidence," it said.

But although the publisher has already sacked one of the two men arrested yesterday – Ian Edmondson, the NOTW head of news, who was dismissed in January – the other, the NOTW's chief reporter, Neville Thurlbeck, has remained a key and active member of its newsroom.

The Met's new investigation team will now seek to ascertain whether the two men were part of, or knew of, a culture of phone hacking at the Sunday paper that went beyond Goodman.

Detectives already have access to a treasure trove of information seized during the original police investigation after a raid in 2006 on the home of Glenn Mulcaire, the private investigator on the NOTW's payroll who was jailed for six months for hacking into voicemails. These detailed notes, along with thousands of emails recently uncovered by News International, are to be made available to lawyers acting for a long queue of celebrities, including Sienna Miller and Steve Coogan, who believe their phones were hacked by the NOTW and are taking legal action against Murdoch's company.

The biggest question is how far up the chain of command at News International the phone hacking goes – and whether the questioning of Edmondson and Thurlbeck will lead to further arrests.

Last week Rupert Murdoch announced that his son James, who has been in charge of his British operation since the hacking scandal re-emerged two years ago, would relocate to New York. It means that the media empire's most senior full-time executive in London will be Rebekah Brooks, a former editor of the News of the World. Ms Brooks has some explaining to do herself as the deadline approaches for her to reply to the Home Affairs Select Committee about how her paper paid police officers for information.