Lucky Gattellari, who's accused of plotting to defraud Ron Medich of millions of dollars, told police the "Medich camp" had approached him about changing his evidence in exchange for up to $15 million.
Detective Senior Constable Mena Wolsely testified that Gattellari later handed him handwritten notes, one of which included: "I would love to get this prick Medich with his hands in the till paying me off".
The notes from Gattellari, who was in Cooma jail at the time in March 2014, also included: "I have done my duty and reported the incident" and "I intend to do nothing inappropriate", while another was headed "Trap for Ron Medich with Roger Rogerson".
He was giving evidence on Tuesday in the NSW District Court trial of Gattellari, 68, who has pleaded not guilty to conspiring in 2013 and 2014 to defraud his former friend Ron Medich, who had been arrested for the 2009 Sydney murder of businessman Michael McGurk.
Gattellari's one-time cellmate, Shayne Hatfield, 53, and Hatfield's former partner, Linda Monfrooy, 55, have pleaded not guilty to being part of the 2014 plot.
The Crown alleges Gattellari, who was also arrested over Mr McGurk's murder, had a "continuing objective" to obtain money through approaches to Medich's family regarding evidence he would give as a crown witness in Medich's murder prosecution.
Det Wolsely said Gattellari told him and another officer in March 2014 that "he had been approached by the Medich camp to change his evidence in exchange for $10 million and that after the committal it would be $15 million".
He testified that they told Gattellari "don't do anything" and "nothing has been authorised", but Det Wolsely agreed police made no notes of this instruction.
In one note given by Gattellari to Det Wolsely, he said he had done his duty in reporting the Medich approach, but unless he got some kind of assurance on his future and jail placement he was not prepared to go any further.
"I will do what I have agreed to do for the DPP to the best my health and mental state will allow me, as for any further involvement in this Medich thing I think I should probably take some legal advice."
He writes of previously telling two other detectives of the "possibility of Mr Medich making an offer to ensure he would not be convicted" and of assuring them he would notify them if it happened.
In the Trap for Ron Medich with Roger Rogerson document, Gattellari said he and Hatfield had devised a plan to "use a connection of Shayne's".
Later he wrote: "I also believe that Roger is doing a back flip and has done a deal with the Mediches to bring me undone and be paid I guess much less than 15 mil".
The trial is continuing before Judge Penelope Hock.