Here's my take....take it or leave it...
A small explosion (let's face it, it could have been MUCH worse: ampho or C4) with easy-to-come-by anti-personnel fragments (ball-bearings according to some reports) sounds like a lone wolf or cell operation. It does not sound like an organized/well-funded attack like 911. McVeigh did way more damage than this. This kind of thing is right out of the anarchist's cookbook and in line with certain domestic attacks that occurred with labor-related terrorist attacks in the past.
My bets are on an isolated Islamic extremist or some nutjob self-labeled "patriot" like McVeigh.
are you saying that you think that was anfo or c-4?
mcvieigh had a government target, this was not aimed at the government.