But the commission conceded that it might have been better to have done so as part of the original inquiry.
"The whole point of the PCC is that the buck stops with the editor," said Tim Toulmin, director of the PCC, in evidence to the Commons Committee for culture, media and sport following allegations made in the Guardian last week.
People have 'raised eyebrows' that Coulson, who is now director for communications for the Conservative Party, was not aware of what was going on, he said.
"He clearly should have known that people were involved in conspiring to break the law. But he didn't apparently," said Toulmin.
"The buck stops with the editor and he resigned. They certainly should know about it and put a stop to it [criminal activity].
Toulmin conceded that there were 'some new facts' that the Guardian's reports had brought to light, such as Gordon Taylor's private court settlement with News International, but the PCC had not yet uncovered any evidence that there have been further breaches of the code from those reported in its 2007 inquiry.
He added that he was aware people suggested information had been sought illegally in the past, but they say it 'absolutely does not take place now', he said.
"I can only say that over the years I have heard rumours that it was the case (...) We will be writing to the paper once we have as much information we can possibly lay our hands on," he added.
The PCC, the effectiveness of which has recently been scrutinised by the select committee and was the subject of a critical report by the Media Standards Trust earlier in the year, last week announced that it would look into re-opening an investigation: 'any suggestion that further transgressions have occurred since its report was published in 2007 will be investigated without delay', it said.
In addition, the body said it would begin to investigate 'the older cases, which suggest the Commission has been misled at any stage of its inquiries into these matters'.
When asked to comment on recent media statements that such practices are rife, Toulmin said: "I think it's very depressing people think it's widespread and common, and journalists routinely engage in that activity.
"Anecdotally, we hear it used to be more widespread, but action has been taken (...) Of course it's easy to condemn historical transgressions."
When asked if such practices continued, he said the PCC could not be 100 per cent sure without having 'some kind of God-given power' to see into journalists' minds.
Toulmin dismissed a Private Eye report about private investigator, Glenn Mulcaire, allegedly being paid £200,000 after his conviction by the News of the World in an exchange for his silence, as the 'sort of nugget' that would be useful for the PCC know.
"There are things that go on at newspapers that people might want to know about (...) I don't think it's fair to expect the PCC to hoover up every allegation about a journalist or a freelancer," Toulmin said.
He said the Information Commissioner had not published names of journalists during the Motorman inquiry, which looked into the use of private investigators by UK journalists, since individuals had not been charged with any offence, and the journalists had not had chance to defend themselves.
The PCC's concern, he said, is dealing with breaches of its code, which include accessing private records or tapping phones. Any instances would only be defensible if in 'serious public interest', he said.
Evidence was then provided by Nick Davies, the journalist behind the Guardian's main reports; Alan Rusbridger, editor-in-chief of the Guardian; and Paul Johnson, the paper's deputy editor.
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