The killing of Tom Oliver in Co Louth in 1991 was one of the more shocking murders associated with the Troubles.
The IRA claimed he was an informer, a charge his family deny.
In 2017, the gardaí re-investigated the murder and the team believed they had advanced the case.
However, the case is now the brief of a British operation investigating collusion, called Kenova. But why has there been no prosecution?
And what do two former British agents in the IRA know about the murder? And what does the garda commissioner know about it through his former role in the PSNI?
Retired chief superintendent John O’Brien spoke on the podcast about a case that plumbs some murky depths and for which Mr Oliver’s family have not received any answers.