The 12 men and women who will over the next few months sit in judgment of Conrad Black are expected to be subject to a dizzying array of high-profile witnesses who were once friends and sat on the board of Hollinger International at the behest of the one-time media mogul.

The prosecutors may call several well-known characters to testify against Lord Black, including Henry Kissinger, but the most influential testimony is likely to come from a man is who far from a household name.

As was the case in the trials against the chief executives of Enron and WorldCom, prosecutors are expected to base much of their case against the British peer on the word of a convicted felon who has admitted that he had a role in the alleged fraud at the newspaper publisher.

David Radler struck his first deal with Lord Black in 1969, when the pair bought a small Canadian newspaper called the Record.

Over the course of three decades, Mr Radler would become the Hollinger chairman’s closest confidant and chief operating officer of their media empire. While Lord Black became the public face of Hollinger, Mr Radler, who became publisher of the Chicago Sun-Times, kept a lower profile, gaining a reputation as an unyielding cost cutter who once said his chief contribution to Canadian journalism had been “the three-man newsroom” – where two sold ads.

When minority investors in 2003 began agitating for change in Hollinger’s two-tiered voting structure and demanded an end to the payment of tens of millions of dollars in management fees to Lord Black’s circle of advisers, the executives did not waver.

But as financial pressure on the individuals – and Hollinger – mounted, culminating in the forced sale of the UK-based Telegraph titles and, eventually, the initiation of a criminal investigation by the office of Patrick Fitzgerald, the US attorney for the Northern District of Illinois, the bond was broken.

In 2005, Mr Radler pleaded guilty to fraud charges and promised to co-operate with prosecutors. A few months later, an indictment alleging fraud was handed down against Lord Black.

“You would assume that [Radler] knows an enormous amount about Black. On the other hand, he also now has an enormous incentive to say things about Black because this is his ‘get out of jail free’ card. This is a guy who’s singing for his supper,” says David Gourevitch, a New York-based defence attorney.

Mr Gourevitch says juries in recent white-collar crime cases have had a tendency to believe government witnesses, even those convicted felons who co-operate with authorities in exchange for a lighter sentence.

The key to making a co-operating witness credible, Mr Gourevitch says, is for the government to corroborate as much of the testimony as possible with other evidence, such as documents or testimony from other witnesses.

Lord Black’s defence attorneys, in turn, will have to try to persuade the jury that Mr Radler lacks credibility and are likely to focus on Hollinger’s board of directors, who Lord Black has said were aware of the transactions that are now under scrutiny. His defence will be boosted by the fact that prosecutors themselves have acknowledged that some of the transactions in question were brought to the attention of the board.

To deflect Lord Black’s defence, legal experts familiar with the case say prosecutors are likely to call some of the board members to testify that Lord Black and other former executives routinely misled them.

Anton Valukas, Mr Radler’s attorney, declined to comment. In an e-mail, Lord Black also declined to comment on Mr Radler’s role in the case. Legal experts have drawn similarities between the case against Lord Black and the trial of Dennis Kozlowski, the convicted former chief executive of Tyco.

Experts say that, like the case against Mr Kozlowski, prosecutors may put Lord Black’s lavish lifestyle on trial – a tactic that can prejudice a jury against a defendant by adding colourful details to the central fraud charges.

But Mr Gourevitch warns that the strategy can backfire, as it did in Mr Kozlowski’s first hearing, which ended in a mistrial.

“In the [Tyco] case, there was a real effort to wind up the jury, there was a view that if you showed a jury the level of excess and wealth, that the jury would not relate to it – that failed, and failed rather colossally,” he says, adding that jurors found the tactic demeaning.

Jurors, legal experts say, want to hear evidence that a defendant broke the law, not just anecdotes describing how extravagant an alleged white-collar criminal’s life may have been.

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