Twenty years ago I got access to secret information which exposed how gardaí stopped investigating the fatal shooting of prison officer Brian Stack within two months of the gun attack in March 1983. Breaking that story began a two-decade long search for answers by the Stack family, which culminated in this week’s State apology for the failings and shortcomings in the garda investigation. But just why the case was so badly handled remains unclear. I remember where I sat, trying to hoover up as much information in my mind as I could manage. It was late 2006, and I was in a room…