‘And so it was that, on the evening of August 4, 1982,’ writes Mark O’Connell halfway through this gripping portrait of double killer Malcolm Macarthur, ‘the Irish government’s most senior legal official had his housekeeper prepare the spare room for his friend, a man who had just days previously murdered two strangers, and who had that very evening botched an armed robbery at the home of an acquaintance.’

The police arrested Macarthur at the flat nine days later. The morning after, the innocent and bewildered attorney general, Patrick Connolly, having cleared it with the police and Charles Haughey, the Taoiseach, set off for a long-planned holiday in New York. The story had broken by the time he arrived. Ireland was in uproar and Connolly was hounded by reporters (the New York Post would run the headline ‘Irish Biggie Flees Here After Slay Scandal’). Haughey summoned him back to Dublin, where he resigned from the tottering government. Haughey described it as ‘a bizarre happening, an unprecedented situation, a grotesque situation, an almost unbelievable mischance’. Haughey’s merciless enemy Conor Cruise O’Brien shuffled his adjectives to create the acronym by which the murders are still known: GUBU.

Macarthur’s partner, son and friends and the nation as a whole were left trying to figure out why an elegant, inoffensive man with impeccable manners had hammered a nurse to death while stealing her car and shot a farmer in the face with the shotgun he was trying to sell.

O’Connell has long been fascinated by Macarthur, a suave, well-spoken, self-described ‘private scholar’, stylishly turned out in ‘tasteful brogues’, Harris tweeds and silk bow ties or cravats, who lived comfortably on family money and whose ‘conversation was filled with long, detailed monologues on such diverse topics as tectonic plate theory, linear regression modeling in economics, the philosophical problem of free will and determinism, the absurdities and complexities of the Irish legal system, and the root causes of the civil war in Vietnam’. He moved in literary circles and in a hard-drinking culture never lost control of himself. ‘His life was a project of refined hedonism,’ O’Connell says.

But when he ran out of money, he was not prepared to work for a living or to ask his cold mother for help. Taking inspiration from the IRA, which was augmenting its war chest by robbing post offices and banks, he planned a robbery of his own, aiming to steal the shotgun that Donal Dunne, a farmer in Edenderry, had advertised as being for sale. Needing transportation to get to Edenderry from Dublin, he stole Bridie Gargan’s car. It was all carried out so ineptly that he ended up pointlessly but brutally killing them both. He exhibited, says O’Connell, ‘the peculiar foolishness of the intellectual. If there is such a thing as a criminal dilettante, this is what he is.’

To widespread public outrage, no evidence was presented in court, for Macarthur pleaded guilty to Gargan’s murder and there was a nolle prosequi for Dunne’s, which spawned innumerable conspiracy theories that would almost bring down the government. The continuing public fascination with him, says O’Connell, ‘draws much of its strength from paradox: Malcolm Macarthur, the genteel brute; the savage intellectual’.

O’Connell’s obsession began when he was working on a PhD on John Banville. He became fascinated by the narrator-protagonist of his The Book of Evidence, shortlisted for the Booker Prize, a character loosely but clearly based on Macarthur. There have been other novels, a play and two well-regarded podcasts about Macarthur’s life. At times when he was being considered for parole – which he was finally granted after thirty years – the media would regurgitate the shocking story with headlines about the ‘Gentleman Killer’ or the ‘GUBU murderer’. He was freed in 2012 and can now be seen at literary events or walking the streets, where he is sometimes challenged by members of the public.

Macarthur cooperated with O’Connell on this book, but getting truly to know ‘who and what this man was’ proved impossible. He is unknowable. He seems never to have belonged anywhere. Of second-generation Catholic Scottish stock, whose oddities were lazily classified by contemporaries as Anglo-Irish, this only child was born and brought up in Ireland by a violent father and a distant mother. O’Connell notes that ‘it was his custom … to refer to “the Irish” as though they were a foreign people among whom he had lately found himself, and of whose peculiarities he had become acutely aware’.

The judgements he expressed in conversation with O’Connell are sui generis. Accounting for his refusal to express remorse or in any way emote about the murders, he said: ‘I regard the Irish as a slightly unctuous culture. As one of the world capitals of unctuousness, in fact. I don’t object to it, but I do like a more restrained approach. You could even call it a more dignified approach, though I don’t want to make too big an issue of that. That’s just my outlook.’

He seemed to stand apart even from himself, for whom he had ‘high regard’, although he regretted what he called the ‘criminal episode’. He had been lucky, he explained, that he had never needed to earn a living, for with inherited wealth ‘you become the master of your own days’. Yet he robbed his victims, whom he called ‘the deceased’, of ‘their time – their freedom, their possibility, their lives – because he could not countenance relinquishing his own’. What O’Connell ceaselessly sought from his subject was an admission ‘not just to having committed murders, but to being a murderer … I wanted to penetrate the carapace of self-possession and stoic composure, and to arrive at something painful and meaningful and true.’ Yet, fluently and politely, Macarthur led him into ‘a labyrinth of endlessly ramifying fictions’.

From this increasingly hopeless quest, thanks to his relentless curiosity, integrity and wonderful prose, O’Connell has created a superb book.