Former News of the World executive editor Neil Wallis will give evidence to the Leveson Inquiry for a second time today.
Three senior figures in the Metropolitan Police have resigned over their links to Wallis, who has been arrested on suspicion of phone hacking.
Commissioner Sir Paul Stephenson and assistant commissioner John Yates stood down last July, and the force's communications chief Dick Fedorcio quit last week.
They all faced criticism over the decision to hire Wallis to provide PR advice for the Met on a £24,000 contract lasting from October 2009 to September 2010.
The Leveson Inquiry heard in February that Mr Fedorcio invited people from leading PR firms Bell Pottinger and Hanover to submit rival bids for the work.
Chairman Lord Justice Leveson suggested that the Met head of public affairs chose these companies because he knew they would be more expensive than Mr Wallis, adding: "The point is, this is set up to get a result."
Fedorcio denied this, but confirmed that he initially wanted to award the contract to the former News of the World executive without any competition.
Yates has told the inquiry he was "good friends" with Mr Wallis, and attended football matches and dined out with him.
Skegness-born Wallis, who first gave evidence to Lord Justice Leveson in December, worked at the Daily Star, The Sun and the People before being appointed deputy editor of the News of the World in 2003.
He became the News of the World's executive editor in 2008 and retired from the paper in July 2009.
Wallis was arrested last July as part of the Met's phone hacking investigation, known as Operation Weeting. He was bailed and has not been charged.
The inquiry will also hear evidence today from Stewart Gull, the detective who led the hunt for the "Suffolk Strangler" who killed five prostitutes in Ipswich in 2006. He is now Jersey Police's head of crime.
Former News of the World crime editor Lucy Panton will appear tomorrow, and on Wednesday testimony will come from current Director of Public Prosecutions Keir Starmer and his predecessor Lord Macdonald.
Prime Minister David Cameron set up the Leveson Inquiry last July in response to revelations that the News of the World hacked murdered schoolgirl Milly Dowler's phone after she disappeared in 2002.
The first part of the inquiry, sitting at the Royal Courts of Justice in London, is looking at the culture, practices and ethics of the press in general and is due to produce a report by October.
The second part, examining the extent of unlawful activities by journalists, will not begin until detectives have completed their investigation into alleged phone hacking and corrupt payments to police, and any prosecutions have been concluded.