My opinion on the proposition that prisons contribute very little to the radicalisation is that gangs are too dominant and powerful and personal survival often centers on some degree of attachment to an established group/gang. There probably isn't enough literal and figurative space for a radical Islamic cell to thrive. I also note that immediately after 9/11, there was a blurb in the news on how much money convicts in the prison systems had donated. The general prison populations may not be very accepting of a group whose power base is not related to drugs, extortion and profit. With a Quaran in every cell and an established prayer space on hand ( Masjid) it remains possible for a jihadist to at least keep his faith active and accept the inhibition of direct action imposed by confinement.

I found it very odd the huge conversion discrepancy between Europe and the US. Rouhgly 43% here at home had converted from Christianity to Islam compared to roughly 18% in Europe.