They may have had some kind of training, but I don’t think the “complexity” of the bombs is any evidence of that. A Freeper who claimed to be an electrical engineer posted on a thread in the days after the bombing and said he thought these were very simple devices — and were extremely dangerous even to the bombers themselves because the remote-control car activation method had very high risks for random detonation.
McCaul referred to a level of “sophistication”. Could call it complex I guess, considering the danger and risk involved in preparing the bomb. I think more on the mark is the fact that, “homemade bombs built from pressure cookers have been a frequent weapon of militants in Afghanistan, India and Pakistan. Al Qaeda’s branch in Yemen once published an online manual on how to make one”. Maybe the bombers got hold of the manual and followed the directions, but I doubt it because they didn’t blow themselves up. These guys were one notch up from being considered kids - 19 and 20-something, and definitely not electricians. I still say follow the money. Someone supplied the cash - for the trip to Russia, and for the bomb-parts.