Jonathan Mathew, along with former Barclays traders Stylianos Contogoulas, Jay Merchant, Alex Pabon and Ryan Reich, has been charged with conspiracy to defraud on allegations of conspiring to manipulate US-dollar linked Libor between June 2005 and September 2007.
In his closing argument, William Clegg, the defence lawyer for Mathew, told the court that his client was unlikely to have been recruited to any Libor-rigging conspiracy by his boss, Peter Johnson, adding "you must realise that this was for [Johnson] a huge secret" that he could ill-afford to let anybody else know about.
"The danger of exposure was enormous," Clegg added.
Johnson pleaded guilty to conspiracy to defraud in relation to Libor in October 2014.
In particular, the defence pointed out that Mathew, who was said to have received trader's requests for rates on just 28 days during the indictment period, did not change the rate he had submitted the first time he received a request to do so from a trader, which had happened while his boss was away.
However, the second time such a request was put to him, Mathew did accommodate. This apparent change of heart lead Clegg to conclude that what most likely happened was his client spoke to his boss to ask how to treat such requests and his boss told him to take them into account.
The defence team for Mathew also stressed the importance that the former submitter had been told to only accommodate the request in so far as they would still fall within the range of possible rates provided by the brokers.
Meanwhile, John Ryder, the defence lawyer for Contogoulas, stressed to the court that his client had not appreciated at the relevant time that what he was doing was dishonest, adding that, thanks to the talented computer scientist being assigned to IT projects when he first joined Barclays, he had very little experience in trading by the time he joined the US dollar desk.
"He must have known next to nothing," the barrister remarked of his client's early trading experiences as the bank.
The trial, which started in April, is currently being heard in Southwark Crown Court. The case is the third to go to trial as a result of the Serious Fraud Office's ongoing investigation into Libor.