Holding people above suspicion because they are the favourite terrorist organisation is wrong.

It would indeed be wrong. Obviously the IRA is under suspicion. However, they aren't the only ones.

For example: breakaway Republicans raising funds; one-time IRA people using the skills they have acquired; the recognised loyalist paramilitaries; breakaway loyalists; ex-loyalist paras who've gven up on the politics, but are still into the crime; there could even be ex-IRA and ex-loyalist professional gangsters, in it together for the money. Then there's freelance military or police, from either side of the border; or dirty tricks from within the security services, authorised or unauthorised...

Some of these are far-fetched, some less so - but the thing is, nobody actually knows. And the officials who say they do know, but who haven't produced a shred of evidence, cannot be assumed to be trustworthy.