He has been hailed a martyr for Isis but all right-think people in Ireland – Muslims and Christians alike – will see his murderous attack as monstrous and wonder how a born and bred Dubliner could have become so radicalised.
It would be easy to dismiss his journey from family man with three children to jihadist as the product of a deranged mind but the reality is that he is not alone and there may be more radical extremists among us.
We on the island of Ireland know more about extremism and terrorism than most of our European neighbours. Thirty years of bloodshed north of the Border has seen to that.
But the difference between IRA and INLA terrorism and what we have come to view as Islamic terrorism is that the overwhelming majority of Irish people, north and south, never wavered in condemning loudly atrocities committed in our name, even while acknowledging discrimination against nationalists in the North.
Successive Irish governments did the same and it was this joint approach, as much as the willingness of moderate Unionists to compromise, that allowed reason to emerge and the Northern Ireland peace process to achieve what it has.
Unless the voice of moderate Islam is heard clearly and unequivocally to condemn the murder of the innocents, these cowardly suicide bombings will continue and it is possible that they could happen in Ireland.
That voice is being quelled in many parts of the Arab world, including US allies like Bahrain and Saudi Arabia where democrats and moderate Muslims are routinely jailed.
What is less understandable is why the voice of moderation is so muted in Ireland, the UK and other European states where peaceful protest is viewed as a civic right, not a crime.
In response to Kelly’s suicide attack, Shaykh Umar al-Qadrin, an imam who chairs the Irish Muslim Peace and Integration Council, focused on security, saying: “I personally cannot understand how someone like him wasn’t locked up for openly calling on others to commit atrocities.”
He may have felt constrained in uttering outright condemnation of Kelly by his experience when he spoke out against the Brussels attacks in March and suffered online abuse as a result. Nevertheless, it is essential that the voice of moderate Islam is expressed loud and clear not just by religious leaders but by the majority of the 50,000 Muslims living in the Republic. They have a responsibility to ensure that these attacks are not being done in their name. If they do, it will renew respect for their beliefs and stem the growth of Islamophobia.
Even during the height of paramilitary violence in Northern Ireland, it was the voice of peace uttered by ordinary Irish citizens that finally put an end to the bomb and the bullet.
At the end of the day, it is not the pen but the heart that is mightier than the sword – even the Sword of Islam.