And this conclusion is based on..............?
It's based on the collective achievement of the Arab world? Don't you think, that with these guys' explosives laboratories blowing up all the time, that they're not the brightest lighbulbs in the arena? Whenever they try to go for radioactives we end up catching mortally-irradiated jihadis, too.
On the other hand they seem to be quite prolific with regular explosives and chemicals... like in the 1993 WTC attack, or more recently in the attack on Amman.