Maybe it was an IRA operation, maybe it wasn't. But unfounded allegations mean bugger all. Or rather they just mean there is some political game being played.

The police knew who did the Birmingham bombings didn't they? And the government knew all about these non-existent stocks of WMDs in Iraq?

Trusting any of these guys is always likely to be a step too far. Sometimes they get it wrong, and say more than they know; sometimes for policy reasons they say things they know aren't true.