"It's interesting to note that links with other groups in the past were constructed on a personal basis," says O'Halpin. "So there are hundreds of foot soldiers out there with favors to repay members of other groups, including groups that haven't yet headed for political solutions."
Sleeping With Anyone
Allegations of links between dissident Irish republicans and Palestinian militant groups abound. Last April, a Red Cross explosives expert based in the West Bank refugee camp of Jenin told British newspapers he found pipe bombs in the restive Palestinian refugee camp identical to those he encountered in Northern Ireland.
"When I saw the bombs, it was a flashback to Northern Ireland. The way the pipes were cut and the whole design of the pipe bombs is exactly the same," Paul Collinson told The Sunday Telegraph.
Israeli security experts also believe a West Bank sniper who killed 10 Israeli soldiers and settlers in March 2002 had links to IRA members.
But while the PLO and IRA during the 1980s had symbolic ties as secular nationalist revolutionary groups, the ideological links between the IRA and Islamist Palestinian groups such as Hamas and the Palestinian Islamic Jihad tend to be more complicated.
According to Jeffrey Bale of the Center for Proliferation Studies at the California-based Monterrey Institute of International Studies, links between the IRA and Islamist Palestinian groups could be based on a so-called shared opposition to the Israeli occupation of Palestinian lands or more simply, IRA militants could just be "paid guns."
But allegations of links between the IRA and Palestinian Islamic groups do not surprise O'Halpin.
"All these groups are promiscuous," he says. "They sleep with anyone — the next morning there's a rose on the pillow and they're gone — or a shamrock on the pillow."
The Cuba Connection
Although the IRA and FARC do not share a past history of links, some experts suggest the ties alleged in the latest court case may have been forged for mutually beneficial reasons.
While the IRA has years worth of experience in urban terror tactics, Colombia's drug-running guerrillas are believed to be flush with narco-dollars.
For its part, the IRA has repeatedly denied it had any "military" involvement in Colombia.
But in a June 2002 report, the BBC quoted a British security assessment as suggesting the IRA's activities were "cleared by people at the top of the organization."
The IRA involvement in Colombia, the report adds, was part of a Provisional IRA plan to use Colombia as a "training ground to carry out tests" of new devices and weapons.
Experts suggest the Colombian connection has grown out of old IRA links to Cuba, where a number of IRA men and women on the run are believed to have sought refuge and acquired, among other things, excellent Spanish language skills.
One of the three Irishmen arrested in Colombia, Niall Connolly, is a fluent Spanish speaker who has lived in Cuba.
Cuban authorities have confirmed Connolly lived there as a Latin American representative for Sinn Fein. However, Sinn Fein denies he is a member of the party.
With a verdict expected soon, the mystery of the three Irishmen in Colombia is inching closer to being solved. But it could open up another can of worms in the world of shadowy international links between militant groups of various stripes and persuasions.