The documents bolster claims that high-ranking executives of Murdoch's News Corp. global media empire were aware that phone hacking was more widespread than they let on.
British lawmakers investigating the hacking scandal that incensed the British public, prompted the arrest of over a dozen journalists and forced Murdoch to shut down the News of The World released a copy of the opinion provided to Murdoch's company and lawyers by lawyer Michael Silverleaf in 2008.
In it, Silverleaf says there is "overwhelming evidence of the involvement of a number of senior ... journalists in the illegal inquiries."
At the time, the newspaper was being sued by soccer players' association chief Gordon Taylor over alleged phone hacking.
Silverleaf wrote in his opinion that News Group Newspapers, publisher of the News of the World and referred to as NGN, should increase its offer for a settlement with Taylor.
Silverleaf said "at least three" journalists appeared to have been "intimately involved" in illegal research into the affairs of Taylor. In addition to spying on Taylor, Silverleaf noted "substantial surrounding material" documenting the extent to which reporters tried to gain illegal access to information about other individuals.
"In the light of these facts there is a powerful case that there is (or was) a culture of illegal information access used at NGN in order to produce stories for publication," he wrote.
The newspaper later settled with Taylor out of court for 700,000 pounds ($1.1 million).
Executives at News Corp. insisted until early this year that phone hacking had been the work one rogue reporter. Murdoch shut down the tabloid in July, after evidence emerged that the practice was much more widespread and the British public was outraged at his journalists' hacking into the phone of a murdered schoolgirl.
The scandal has claimed the jobs of top Murdoch executives in the U.K. and the U.S., and forced the resignations of Britain's top two police officials and Prime Minister David Cameron's communications chief.