When trying to analyze any link between terrorism and education one should ask "educated at what?" Education is not one vast, undifferentiated thing. Nor is it necessarily done only in a formal environment. While some technical expertise may be neccessary, as pointed out most terrorist technology is not exactly rocket science. You don't need a PhD in chemical or electrical engineering to make a bomb, for example, even a big one.

Perhaps the most important education is one in the society in which one operates. The ability to blend in and knowledge of how to operate within the target society are arguably the most important kinds of education one can acquire. Most people know most about the society in which they grow up, though even there knowledge varies. Knowledge and skill in operating in foreign environments tends to be more rare and harder to acquire. This is one of the reasons many terrorist groups can operate efficiently on their 'home turf' but have problems carrying out any type of extended/complicated interational effort.

Thus, a someone raised as a barely literate shoe-shine boy in Bagdhad may be a more effective terrorist in Iraq than a Georgetown area studies MA. Aguable, the hardest part of terrorism is the "operational art" of actually carrying out attacks in the real world. That is not something typically taught (at least directly) in most educational settings.