The participants fabricated accounts both “to cover the tracks” of those responsible for the killing, and “the careless military outfit that let it happen.”

After Piaras Beaslaí’s two-volume biography in 1926, little was written about Collins until Frank O’Connor published The Big Fellow in 1937, followed by Rex Taylor in 1958. This publishing indifference probably explains why so little was written about Collins in the 40 years after his death. I cannot remember ever hearing his name mentioned in school in Tralee during the 1950s and early 1960s.

But I later became intrigued by his life while studying for a doctorate in history at university in Texas.

In 1977, after writing a book on Irish neutrality, I was commissioned by Gill & Macmillan to write a short biography of Éamon de Valera for their Irish Lives series, which came out in 1980.

When asked afterwards, I indicated that my next book would be on Michael Collins, but Gill & Macmillan felt there would be no commercial interest in him. Tim Pat Coogan was told the same thing when he tried to interest them in his biography of Collins.

Such publishing indifference probably explains why so little was written about Collins until Eoin Neeson wrote the Life and Death of Michael Collins in 1968. Neeson suggested Collins was killed by a ricochet bullet, which could have been fired by one of the Republican ambushers, or accidently discharged by John McPeak, one of the Free State soldiers. The book, published by Mercier Press, sparked interest in the death of Collins. There had been no proper autopsy, or even any adequate report of what actually happened.

As a result, speculation mounted and became as intriguing as the conjecture surrounding the death of US president John F. Kennedy over 40 years later.

In 1981, John M. Feehan, the founder and publisher of Mercier Press, wrote The Shooting of Michael Collins: Murder or Accident? He essentially dismissed Neeson’s ricochet story.

Feehan believed six different witnesses saw a small entry wound in Collins’s forehead. He suggested Collins may have been murdered by one of his own colleagues acting on behalf of members of the Provisional Government, or the British Secret Service.

According to Feehan, a junta within the Provisional Government conspired against Collins. This was reputedly headed by the man that Collins had supposedly called “that bloody little altar-boy” — W.T. Cosgrave.

This junta allegedly included Kevin O’Higgins, Ernest Blythe, and evernDick Mulcahy, according to Feehan.

Neeson dismissed this theory as “clearly nonsense”, but then even Feehan himself deemed it “most unlikely”. He went on to suggest, however, that Emmet Dalton may have killed Collins on behalf of the British Secret Service. However, he did not present a shred of supporting evidence. Feehan repeated Neeson’s allegation that Defence Minister Desmond Fitzgerald ordered the Army to destroy files relating to the death of Collins, as Fianna Fáil was about to come to power in 1932. This was refuted by Colonel Dan Bryan, who supervised the destruction of Army documents. He was adamant that no files relating to Collins were involved.

In The Day Michael Collins was Shot, a much more plausible book in 1979, Meda Ryan rejected suggestions that Collins was killed by one of his own men. She contended that Sonny O’Neill, one of the ambushers, fired the fatal shot, without recognising his target.

In his 1991 book, The Dark Secret of Béal na Bláth, Fr Patrick J Twohig also contended that Collins was killed by one of the Republicans. Mike O’Donoghue, an IRA intelligence office from Glenflesk, happened to be passing the ambush scene with his friend, Bob Doherty, on their way home to Kerry. Seeing a Free State officer standing on the road, Doherty fired a shot at him.

“We saw the big man fall,” O’Donoghue recalled. He promptly slapped Doherty’s gun down. “What did you do that for?” he snapped. “Do you want to draw them on us?”

With that, they both “skedaddled”. They had no idea of the identity of Doherty’s victim, but Fr Twohig believed it was Collins.

In her 2010 book, The Assassination of Michael Collins, S.M. Siegerson attached considerable significance to the fact that Collins was in Cork in the hope of negotiating a peace settlement in the ongoing Civil War with prominent Republicans Tom Hales and Florence O’Donoghue, who had been adopting a neutral stance.

In the latest book on the killing of Collins, Gerard Murphy casts serious doubts on Florrie O’Donoghue’s motives, just as Feehan raised suspicions about Emmet Dalton. Murphy contends O’Donoghue was seeking to implement a decision of the Irish Republican Brotherhood in Munster to execute Collins for treason, because he had supposedly betrayed the Republic.

Murphy argues that O’Donoghue was only pretending to remain neutral in the Civil War in order to set up Collins by offering to negotiate a settlement between the warring sides. He got the Big Fellow to meet him in Macroom on the morning of the ambush, and he then led “Collins into a trap with the promise of a further meeting that evening”.

After leaving Macroom, Collins headed for Clonakilty. Various Republicans stated that he travelled through Béal na Bláth, so they set up an ambush to get him on his return. But Murphy argues that Collins had gone south gone by another road.

If he did not go by Béal na Bláth, why would they think he would return that way? The arguments are not convincing.

If O’Donoghue was really an ardent supporter of the warring Republicans, he was also misleading Liam Lynch, the Republican Chief of Staff. On July 3, 1922, for instance, O’Donoghue wrote to Lynch that, after thinking it over carefully, “there is nothing in the circumstances of the origins of the present conflict which would justify my taking part in it”.

Murphy also argues that Collins was not killed by a ricochet, but by a snub-nosed bullet fired from a high-powered hunting rifle, by an assassin who was targeting Collins specifically. The author states that Oliver St. John Gogarty, who embalmed the body of Collins, wrote that there was a small entry wound on the hairline behind the left ear and the dum-dum bullet then blew out the back right side of his head.

But in an autobiography published in 1954, Gogarty actually stated the wound was caused by a ricochet and there was no other entry wound. He went on to state that Dr. Leo Ahern, who examined the body of Collins at Shanakiel hospital earlier, told him that he saw was no wound, other than the large, obvious one at the back of the head.

Gerard Murphy does not suggest who actually fired the fatal shot.

“It has not been possible to identify the man,” he writes.

“My view is that this is a relatively minor matter compared with identifying the circumstances that brought about his death.”

Unfortunately, this kind of speculation seems likely to continue.

The Great Cover-Up: The Truth about the Death of Michael Collins by Gerard Murphy The Collins Press, €19.99