Five men deny conspiring to extort money for the painting's return
An undercover policeman has told a court about his first contacts with the men accused of trying to extort £4.25m for the return of a Leonardo artwork.
The officer met Liverpool publican Robert Graham - known as the Silver Fox - in a pub at London's Euston Station.
He described the accused as a "loveable rogue" who claimed he was acting out of a "sense of decency".
Mr Graham and four others deny trying to extort money for the safe return of the Madonna of the Yarnwinder.
The masterpiece was stolen from the Duke of Buccleuch's Dumfriesshire estate in 2003.
An undercover officer, known by the alias John Craig, was giving evidence at the High Court in Edinburgh about the first indications the artwork had resurfaced four years later.
He told the trial that Mr Graham had come to a pub meeting in September 2007 thinking he was meeting a representative of the duke.
Mr Craig said he appeared terrified that he might be arrested in connection with the stolen painting and wanted to meet him to make sure he was not "the chief of police".
Mr Craig said that he and Mr Graham swapped "personal details".
"He was the owner of a number of pubs in the Merseyside area and his nickname was the Silver Fox," he said.
"Through his background and ownership of these pubs he learned a lot about what was going on in criminal circles.
"He found out about this painting and that he could retrieve this painting."
The court heard that Mr Graham also brought to the meetings press clippings of himself and associate John Doyle and their crime-fighting organisation, Stolen Stuff Reunited.
The internet-based company had successfully returned a stolen sword to "the family of a military man", which was the story in the newspaper clippings.
The firm went bust after Mr Graham, who had also worked as a private investigator, had sunk £30,000 into the venture.
On trial along with 57-year-old Mr Graham are Marshall Ronald, 53, and John Doyle, 61, all from Lancashire, Calum Jones, 45, from Renfrewshire, and David Boyce, 63, from Lanarkshire.
They have denied conspiring to extort £4.25m and an alternative charge of attempted extortion.
The offence is alleged to have taken place between July and October 2007.
They are not accused of the painting's theft.
The trial continues.