The fiftieth anniversary of the Dublin Monaghan bombings falls on May 17.
Thirty-four people died in the four bombings in what was the worst tragedy in the state since the Civil War.
Families were marked for life by the killings but beyond the human tragedy, there was also a state scandal associated with the day.
Over the years it has emerged that both the Irish and British governments of the day showed no interest in investigating the crime and bringing perpetrators to justice.
Retired senior garda John O’Brien has written a book about the case, focusing on the political and policing elements in the aftermath and why there appeared to be a lack of willingness to find out who had bombed Dublin and Monaghan.
John O’Brien is this week's guest.