One can speculate and speculate and have all kinds of theories about why anyone could have set this one up - I listed a few possibilities up the thread, and I didn't by any means exhaust the range.

But as yet there's no convincing evidence pointing in any particular way. The one thing that is pretty unarguable is that whoever set it up, if they had any political motive (which they may well not have had, in fact), that would have been to try to stymie the peace process, and ensure that there wasn't going to be any administration involving Sinn Fein in the near future.

I'd say that probably rules out the core Sinn Fein leadership and the core British Government leadership - but it leaves an awful lot of other possibilities.