The role of the press is...

Not a source I'll often quote, but in its mea culpa editorial on its publication of lies under the stark front page headline THE TRUTH back in 1989, here's a useful snippet:

The role of a newspaper is to uncover injustice. To forensically examine the claims made by those who are in positions of power.

You can read Roy Greenslade's analysis of the press coverage of the report into the lies and police cover-up of the events around the Hillsborough disaster, when 96 Liverpool football supporters died, at http://www.guardian.co.uk/media/greenslade/2012/sep/13/hillsborough-disaster-sun