Mr Medich, 68, has pleaded not guilty to the murder of his former business associate, Michael McGurk, who was shot dead outside his Cremorne home on September 3, 2009.

Matthew Crockett told the Supreme Court murder trial that in early 2010 his friend Lucky Gattellari had given him the choice of being paid $700 to drive Mr Medich or $1400 to follow Mrs Medich.

Mr Crockett said he chose the latter and for three weeks he followed Mrs Medich trying "to get some dirt" on her.

He said that although it was organised by Mr Medich's then close associate Gattellari, he understood that he was doing the surveillance on Mrs Medich on behalf of her husband.

He also said that Mr Medich had asked him how it was going and he told him he would get a written report to Mr Medich.

Under cross-examination by Mr Medich's barrister Winston Terracini, SC, Mr Crockett agreed that in an early police statement he recounted being at Tuscany restaurant in Leichhardt when he overheard Mr Medich on the phone having a heated argument with his wife. When Mr Medich returned to the table he said, "I should've f….d her off like McGurk."

Mr Terracini put to Mr Crockett that no such thing happened and that when Mr Medich found out his wife was being followed he demanded the surveillance stop immediately.

Mr Crockett denied these suggestions.

He also told the court that he and Gattellari were having their customary morning cognac and cigars on October 13, 2010 when police raided Gattellari's Chipping Norton factory, arresting Gattellari and others over their roles in organising the murder of McGurk.

Several days after the arrest Mr Crockett accompanied Gattellari's son Loren to pass on a message from Gattellari to Mr Medich's son Peter.

Mr Crockett said the message was that unless Mr Medich paid $1 million for Gattellari's legal fees into his solicitor's account, Gattellari would "dob in" Mr Medich.

He said Peter Medich replied: "I can't believe this is happening" and that only several weeks earlier police had asked his father to wear a wire.

Mr Crockett also gave evidence about the debt collecting work that he did for Gattellari, which involved either phoning or visiting people to tell them to pay up "or else."

One of those Gattellari had directed him to speak to was Sydney real estate agent Will Manning who owed $300,000 to Mr Medich.

In his evidence Mr Manning said he had met Mr Medich through their mutual interest in horse racing. But he was vague about how much Mr Medich had lent him, stating there might have been five loans totalling $200,000.

He also borrowed $120,000 from Gattellari, the court heard.

Mr Manning, who worked briefly out of McGurk's York Street offices, said it was during the GFC and he was helping high-net-worth people obtain mezzanine finance.

He told the court that he had no records of the repayments of the loans to Mr Medich or Gattellari.

When Mr Terracini asked how certain he was about repaying Mr Medich, Mr Manning replied: "Very."

The trial continues.