The topic was on NPR the other night, that Iraq was becoming a training ground. It is good also it was pointed out "criminal elements" were involved is some of the actions. For more information check the NPR schedule. It was a very good discussion on it
I'll bet the criminals were not volunteering for the suicide bombings.
I doubt they are training much either. They are freelancing as opportunists in a somewhat chaotic situation, to ransom, steal, kill --whatever strikes their criminal mind fancy.
FWIW, a captain at Mosul wrote me several months ago that the majority of the people involved in violent actions there this year have been criminals.