No one's claimed responsibility but there are some dissident groups. The theory is that it was either the Real IRA or the Continuity IRA, but while they never really went away there does seem to be an uptick in activity.
That's disturbing. Are there any guesses as to the reason behind the increased activity?
The reason I ask is that, while taking an Irish history course a few years ago, I was casting about for a term paper project and came across some interesting connections between some IRA branches and the PLO. Interesting, yes, but I didn't think I had the time to pull that one off. So now I'm starting to wonder about other connection.