The judge in the trial of three former Anglo Irish Bank directors described the bank's former chief executive David Drumm as "the author" of the €450 million scheme designed to prop up Anglo's share price. In the case of two of the men, a jury found the "Maple 10" loans for shares scheme to be illegal.

Drumm’s name featured in many news reports about the case as being “not on trial” or “not before the courts”. His absence must have perplexed the jury who heard his name so often.

Near the trial’s end, a defence lawyer, referring to Drumm’s absence, described the trial as “Hamlet without the prince”.

The 47-year-old former banker moved to the US six months after resigning from Anglo in December 2008 and has refused to return to Ireland to be questioned in the five-year investigation into Anglo.

In light of the jury’s guilty verdicts against two individuals over a scheme Drumm managed and directed, it would be assumed this would strengthen any legal case to extradite him from the US.

It may not be so simple. For a person to be extradited, prosecutors must guarantee that they will face charges once surrendered to Ireland. But if a person is to be extradited, there must be corresponding offences in both countries. This is where any bid to force Drumm’s return may encounter difficulties.

Corresponding offence
In Ireland, section 60 of the Companies Act 1963 prohibits a company providing financial assistance to buy its own shares and last week's convictions marked the first conviction under this 51-year-old law.

In the US there is no direct corresponding offence. There are certain restrictions on public companies, including under the 2002 Sarbanes-Oxley Act, but no similar ban on share lending by private firms.

One famous example of US share lending, dating back to the 1980s, involved George W Bush, later to become 43rd US president, who received two low-interest loans from an oil company to buy its shares.

The deal allowed Bush to raise enough to buy into the Texas Rangers baseball team, an investment that helped the fledgling politician amass his personal fortune and launch his political career in Texas.

“The Anglo verdict doesn’t change anything,” said a Dublin barrister familiar with extradition cases between Ireland and the US. “It has to be an offence in both jurisdictions and that can be tricky.”

Matters may be complicated further by a rule in international law known as the doctrine of specialty, which applies in the extradition treaty between Ireland and the US.

This stops a country prosecuting a person for an offence other than the crime for which they have been brought back under extradition.

Specialty is not absolute, however, and it is possible to prosecute the individual on another offence as long as the United States consents, though the rule does not apply indefinitely.

Still, this rule in the extradition treaty with the US may mean the Director of Public Prosecutions (DPP) could await completion of all the investigation files into Anglo before they proceed with an extradition application, though after five years it may be hard to see what work remains outstanding.

Refusing interview
Other transactions under investigation at Anglo during Drumm's time as chief executive could lead to charges, though gardaí are hampered by his refusal to return for questioning.

The DPP does not deem an investigation complete and ready for charges until investigators have made every effort to interview a suspect and to put the allegations to him to see what, if anything, he might say in his defence.

That is not to say that Drumm cannot be charged without being interviewed; if there is sufficient evidence of a crime, they can charge him. Prosecutors can seek to invoke some mutual assistance procedures from the US allowing them to interview him there. The DPP is reported to be weighing whether to bring charges against Drumm after receiving a file from investigators in late 2011.

While consideration of that issue continues, Drumm faces a trial in Boston next month to decide whether he can walk away from his bankruptcy debts.

In a legal action taken to stop that happening, his former bank said that Drumm arrived in the US with an E-2 Treaty Investor visa in June 2009.

An Irish citizen can obtain an E-2 visa for a maximum of five years, which would bring Drumm’s visa up to June 2014, though he can apply to have his visa renewed.

Judge Martin Nolan in the Anglo trial described Drumm as "a man who knew his own mind". Showing no intention to return to Ireland, and with the potential to remain on in the US indefinitely, Drumm must be brought home if the author of the illegal share lending scheme is ever to be brought to book.