The true story of one of the biggest bank heists in Irish and British history - and the questions that remain.

On a Sunday evening in December 2004, two young men were at home with their families. Both worked for the Northern Bank's cash centre in Belfast. They heard knocks on their front doors. Within a few minutes, masked men invaded their homes, overpowered their loved ones and disabled their electronic devices. It was made clear to the two bank officials that they had a choice: do what they were told or their families would die.

Over the course of the following day, £26.5 million was stolen from the Northern Bank: the biggest cash heist in Irish and British history. The two men whose families were held hostage simply re-labelled vast amounts of cash as rubbish and wheeled huge bags to a van waiting outside in the street, yards from Belfast's City Hall. The robbers' knowledge of the inner workings of the bank was astonishing. They deployed a large crew of drivers, guards, watchers and gunmen.

It was immediately obvious that only one organization had the ability to plan and execute such an audacious, minutely-planned robbery: the Irish Republican Army. But the IRA was supposed to be demobilized as a result of the Good Friday Peace Agreement signed six years earlier. The leaders of Sinn Féin (who were also leaders of the IRA) vehemently denied they had anything to do with it.

No-one believed them. The governments in London, Dublin and Washington were outraged. Yet no one was ever been convicted of any crime relating to the heist and little more than two years later, Sinn Féin was in government in Northern Ireland.

In the wake of the twentieth anniversary of this bizarre robbery, Glenn Patterson builds on his popular BBC podcast to shed new light on the story of the infamous heist, the victims, the organizers and the abortive, at times comically inept, attempts to find the people who carried it out.