Millionaire property developer Ron Medich organised for his then associate Lucky Gattellari to spy on Mr Medich's wife Odetta and to collect debts on his behalf.
Gattellari, 66, who has pleaded guilty to his role in the 2009 murder of Michael McGurk, is the Crown's star witness in the murder trial of Mr Medich, the accused mastermind.
Mr Medich, 68, has pleaded not guilty to the murder of Mr McGurk, his former business partner, and the subsequent intimidation of Mr McGurk's widow, Kimberley.
The Supreme Court jury in his murder trial heard that, for several months in early 2010, Mr Medich was having marital problems and wanted his wife followed.
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Gattellari told the court that Mrs Medich, with whom he had a frosty relationship, was trying to get information about her husband. Mr Medich, in turn, wanted information about her.
Gattellari told the jury that he organised for a young associate, Matthew Crockett, to follow Mrs Medich to see where she went and what she was doing. Gattellari passed the results of the surveillance to Mr Medich.
Gattellari, a former professional boxer, gave evidence that Mr Medich also asked him to chase up money owed to him by two of Mr Medich's friends - Tim Alford and Will Manning - to whom Mr Medich had lent $250,000 and $300,000 respectively.
Gattellari, who had a full-time driver due to his propensity to drink alcohol from the morning onwards, organised for the driver, Senad Kaminic, who had done previous debt collecting work, to "pay them a visit".
He said that, while he stipulated that "no violence be used", Kaminic would have used "quite an unpleasant tone" to press upon them to repay Mr Medich's loans.
The jury also heard that, from 2008 until 2010, Mr Medich poured up to $16 million into a group of struggling electrical contracting companies controlled by Gattellari.
No documentation of Mr Medich's loans was ever made.
From those funds, Gattellari said he made weekly cash payments of up to $10,000 to Mr Medich from 2008 "up until I found myself in jail".
He said the pair spent most of their days together going to restaurants, massage parlours, clubs and the races.
Gattellari also said that Mr Medich had agreed to lend $1 million to his brother Rocky Gattellari, who was in financial difficulties over a development on the Central Coast.
Of that amount, Gattellari said that $370,000 was passed to his brother and the rest went into the electrical company's account.
Gattellari was arrested on October 13, 2010. The jury has heard that within days Gattellari was co-operating with the police and he later provided them with numerous statements, including one that was 431 pages in length.
Gattellari later received a substantial discount on his sentence for agreeing to give evidence against his former close friend.