The IRA’s “armed struggle” was what the fourth Geneva Convention defines as an “armed conflict not of an international character”. Under the convention, the parties to such a conflict are bound to respect certain standards in their treatment of “persons taking no active part in the hostilities”…
It should go without saying that the IRA, partly under the leadership of Martin McGuinness, consistently breached every one of these provisions. But apparently, it does not, so let’s put it on record again. The IRA killed 644 civilians, by far the largest category of its victims (by contrast, and contradicting its self-image as defender of the Catholic community, it killed just 28 loyalist paramilitaries). It incinerated, for example, the members of the Irish Collie Club at the La Mon Hotel. It killed children, including Nicholas Knatchbull, Jonathan Ball, Tim Parry and Paul Maxwell. It practised kidnapping, torture, and acts of naked sadism, such as forcing Patsy Gillespie to drive a van loaded with explosives at an army checkpoint. (Widespread revulsion did not stop the IRA from trying this tactic again.)
It held kangaroo courts and imposed arbitrary sentences that included mutilation through so-called “knee-capping”. All of these are war crimes for which there is no statute of limitations.
I don’t know what personal role McGuinness may have played in any incident. However, what is clear is that he was, for almost the entire period of the conflict, in a position of authority within the IRA. Legally and morally, this makes him responsible.