Heated exchanges have so far marked the wine fraud court battle between collectors Eric Greenberg and billionaire William Koch in New York, as the case looks set to run into next week.

Antipathy between the two men was ratcheted up further this week as Greenberg’s former house manager, Jaime Cortes, gave evidence as a witness for Koch.

From the witness box, Decanter.com understands from a source watching the proceedings that Cortes made clear that there was little love lost between himself and his former employer, who he labelled a ‘tyrant’.

He confirmed that he had referred to Greenberg as an ‘a**hole’ in a previous email, the court heard. Cortes also made reference to his ex-employer’s aggressive behaviour, and suggested that Greenberg intimated he would try to pass suspect bottles on to somebody else after being made aware that he might have counterfeits in his cellar.

During cross-examination, Cortes was portrayed by Greenberg’s team as a jilted employee.

The court also heard this week how four different auction houses warned Greenberg that some of his bottles were likely counterfeit. Greenberg was reported to have reached a settlement on suspect wines with one of his suppliers in 2004, according to a Forbes report of the court case.

The case, being heard in Manhattan Federal Court before Judge Paul Oetken and a team of jurors, was supposed to close by the end of this week, but currently looks set to continue into the middle of the week after.

In 2007, Koch brought the lawsuit accusing Greenberg of knowingly selling him dubious bottles when auctioneer Zachys sold 17,000 bottles from Greenberg’s collection. Koch claims that 24 of the US$3.7m of rare bottles he bought at that sale are dubious or fake.

The key question emerging from the current court case appears to be whether Greenberg knew in advance that some bottles from his collection sent for auction at Zachys were fake, and, if he knew that, whether they were they sent to Zachys deliberately.

After Koch bought the Greenberg bottles, which included ultra-rareties such as 1864 Château Latour, 1921 Pétrus and 1921 Cheval-Blanc, he concluded that seven were ‘counterfeit’ and four ‘possibly counterfeit.’ Greenberg strongly denies wrongdoing, and will have the chance to call his own witnesses in the coming days. The case continues.