History has shown the potential of prisons to serve as incubators for extremist leaders, from Adolf Hitler—who wrote Mein Kampf while in prison—to Abu Musab Al-Zarqawi—whose radicalism hardened during a six-month prison term in the 1990s. In addition, it is common for charismatic radicals to convert and radicalize disaffected prisoners, like convicted “shoe bomber” Richard Reid, a product of Great Britain’s prison system.Could that be occurring in U.S. prisons? Congress recently asked experts that question at a hearing on the issue. The answer, according to a report presented there, was that prisoner radicalization is “a threat of unknown magnitude to the national security of the U.S.”

In testimony before Congress, the report’s co-author, Gregory Saathoff, a prison psychiatrist and head of the University of Virginia School of Medicine Critical Incident Analysis Group, recalled a routine visit he made to a correctional facility a couple days after the September 11 attacks.

“Anxious inmates informed me that televised images of the 9-11 attack were cause for celebration among many of the inmates. In fact, they estimated that a third of the inmates praised the attacks, and their cheers could be heard in cellblock after cellblock,” Saathoff said.

The report, written by a task force representing law enforcement, the private sector, and academia, notes that prison radicalization is by no means exclusive to Islam, but extends also to extremist Christian groups and fascist or neo-Nazi organizations, which in the latter case share common enemies with radical Muslims: Jews, the state of Israel, and the U.S. government.

The religion of Islam, however, attracts the vast majority of inmates who convert to a religion while incarcerated, and the number of practitioners dwarfs that of Muslim chaplains working in the nation’s prison system. One state prison admitted 3,000 religious volunteers in a month, “an impossible number for short-staffed prison officials to monitor effectively,” Saathoff says.

According to task force co-chair Frank Cilluffo of The George Washington University, traditional “Jailhouse Islam,” or “Prislam,” often applies a “cut-and-paste” treatment of the Koran into a radical agenda. The advocates of this radical agenda give prisoners documents like “The Noble Qur’an,” a Wahabi text including anti-Zionist notes and an appendix that calls readers to jihad.

The report’s authors drew sharp distinctions between three types of conversion: constructive religious conversion, conversion by radical sects, and individual radicalization. They noted that the recruitment of just one radicalized prisoner to violent jihad poses a serious threat of home- grown terrorist action.

In an effort to get an early warning about any such prisoner who might be ready to play the role of the martyr, California’s correctional authorities forward information about prison radicalization to the state’s intelligence “fusion centers,” where officials from all three levels of government and the private sector share information, according to the report.

The Federal Bureau of Prisons and the FBI are attacking the problem as well, both by vetting chaplains and religious volunteers, and by closely tracking inmates with suspected terrorist ties.

But there’s no certainty about the size of the problem or the effectiveness of these preventive efforts. The Prison Radicalization Task Force recommends that Congress establish a commission to conduct an objective risk assessment, enabling officials to “address this issue now, rather than forcing them to manage a crisis later.”