I've read editorials and letters, saying essentially the same as that quote from An Phoblact,in mainstream publications which clearly have no sympathy at all for terrorism. They aren't seeking to excuse it, but to warn about the danger of ill-directed retaliation, and identify some contributory factors.

Incidentally, when the quote refers to "the deaths of many thousands of innocent people", and suggests that the US government carries responsibility for them, it doesn't read to me as a reference to September 11th at all.

As for why the man had accumulated all that stuff, that's the kind of thing intelligence people do, they gather everything and anything in case it might be useful for any conceivable reason, no doubt including the contingency that the ceasefire might break down. And no doubt it's the kind of stuff the British Army have for the very same reason - and when gathering it I doubt if anyone worries too much if the law is breached in the process. But it's not the same thing as a breach of the ceasefire.

If it turned out that the IRA had been using information gathered in this way in order to carry out targetted assassinations, that would be the kind of thing that would constitute a breach of the ceasefire. But so far as I know that has not been alleged.