Mark O’Connell’s new book A Thread of Violence is the writer’s attempt to understand Malcolm MacArthur, the figure at the centre of one of Ireland’s most notorious crimes, and — to quote Taoiseach Charles Haughey — the “grotesque, unbelievable, bizarre and unprecedented” events that led to the perpetrator’s eventual arrest in the home of the Irish Attorney General. It is a crime that has haunted O’Connell for decades and which leads him to meeting and getting to know the now elderly, long-freed MacArthur. As this unlikely acquaintance grows, however, O’Connell not only comes to question the possibility of ever coming to any conclusion about what actually drove this previously law-abiding local eccentric to murder two strangers in the summer of 1982, but also calls into doubt his own motivations for embarking on the project in the first place, and the risks he is taking in his own life to complete it.