"It was that greed that led to his dishonesty on an enormous scale," Mukul Chawla, the prosecutor, told the jury.

In the opening of the first trial related to suspected rigging of the London Interbank Offered Rate, or Libor, Chawla said Hayes provided 82 hours of voluntary testimony to the Serious Fraud Office over five months, admitting that he rigged the rates and testifying against many former friends and colleagues.

"I probably deserve to be sitting here because you know I made concerted efforts to influence Libor," the court heard him saying on an audio recording. "My trading book directly benefited from that."

Hayes has pleaded not guilty to eight charges of conspiracy to defraud. He will have an assistant throughout the case because of a diagnosis of mild or very mild Asperger's syndrome, the judge told the jury. His lawyers requested that he not sit in the dock, but in the back of the courtroom, so as to be close to his lawyers and the assistant.

In his opening statements, Chawla emphasised the complex case was in fact quite simple.

"It is about dishonesty," he said. Between September 2006 and September 2010, Hayes "behaved in a thoroughly dishonest and manipulative manner," Chawla said.

The prosecution presented audio clips of Hayes, as well as quotes from his extensive testimony to the fraud office. Hayes will now say that his actions were not dishonest, Chawla said.

"The point is you're greedy; you want every little bit of money you can possibly get," Chawla said, quoting Hayes. "What can I say? That's how you are judged. That's your performance metric."

Chawla explained that Hayes was part of a larger ring of about 25 traders at 16 banks, some of whom face separate trials or are under investigation. Hayes gave evidence against many of his friends and even his half brother, the prosecution said.

'Extremely intelligent'

But it was necessary to try Hayes separately because he was at the "epicentre" and acted as a "ringmaster," the prosecutor said.

"His actions stood apart from and above all of the others," he said.

Chawla described Hayes as an "extremely intelligent man" who was well compensated for his trading prowess. Hayes told the Fraud Office that his trading revenue for UBS, which started at a couple of million dollars in the last few months of 2006, rose to $US89 million ($115 million) - "or something like that" in 2008 and $US150 million in the first nine months of 2009, before he left for Citigroup. In total he made about £1.3 million ($2.6 million) for UBS and £3.5 million for Citigroup, which paid him a large sum to move over.

The prosecutor presented what he expected to be Hayes' defense and tried to dispel it. He cannot contend that he did not rig Libor, because he admitted as much in the substantial evidence provided, Chawla said. But Hayes would assert that Libor rigging was already widespread and known to his superiors, he predicted.

"Just because other people were doing the same thing - even many other people - that cannot make a dishonest act honest," Chawla said.

While maintaining to the jury of seven men and five women that the case is not complex, Chawla conceded that it will be long and involve many documents. The jurors have stacks of notebooks, and multiple screens in the courtroom will display the extensive digital evidence.

He started the painstaking process of explaining what Libor is, how it is set, why it is important, and how Hayes worked with various other traders and brokers to manipulate it. He introduced the concept of an interest-rate swap transaction with statements such as, "It's not as complicated as it sounds."

"Not only will you be able to see the fraud being carried out in the words typed by Hayes in the instant communications and the many messages he sent; you will also be able to hear him from tape recordings that still exist," Chawla said. "You will hear him committing these offenses."

He said that brokers who helped Hayes manipulate Libor were rewarded with "bribes" or so-called wash trades, large orders that are executed just to generate trading commissions. This was a favour "for their help in manipulating Libor," Chawla said.

The trial is expected to last two to three months, and opening statements are expected to last all week.

The New York Times