But how deep and influential are those pockets? And how dangerous? According to two recently published studies, concerns may be overblown about the ability of Al Qaeda or like-minded militants to cobble together terror cells by tapping disaffected Muslim-American prisoners.
"It doesn't seem to be happening. If prisons are incubators for radicalization, you'd think we would have seen it by now," says Bert Useem, a sociologist at Purdue University in West Lafayette, Ind. His three-year study on radicalization appeared in the August issue of Criminology and Public Policy.
Professor Useem and Obie Clayton, a sociologist at Morehouse College in Atlanta, interviewed 210 prison officials and 270 inmates in 27 medium- and maximum-security state prisons. "The claim that prisons will generate scores of terrorists spilling out onto the streets of our cities ... seems to be false, or at least overstated," they concluded.
Similarly, a June article in the British Journal of Criminology, by criminologist Mark Hamm, debunks many post-9/11 theories about prison radicalization, namely the idea that austere Muslim clerics in Saudi Arabia were making inroads with prison converts in America.