¿ Richard Reid, a British citizen and follower of Osama bin Laden, who was a prison convert in England and became involved with militants after he was freed. He pleaded guilty in 2002 to trying to blow up a trans-Atlantic flight with explosives hidden in his shoes. He is now serving a life sentence at a maximum-security prison in Florence, Colo.

¿ A group of prisoners in California who converted to Islam and were arrested in 2005 on charges of plotting behind bars to attack military sites, synagogues and other targets.

Islam took hold in U.S. prisons in the 1940s, when members of the Nation of Islam were held for refusing to fight in World War II. Malcolm X was one of their most famous prison recruits.

The religion spread when Muslim inmates successfully sued for more freedom to practice their faith. Get-tough sentencing laws enacted in the 1980s filled prisons with large numbers of blacks and led to another spike in conversion. By this time, many blacks who once were in the Nation of Islam embraced mainstream Islam instead.

Some inmates gravitate toward Islam out of resentment over being locked up, said Jimmy Jones, a Muslim chaplain and volunteer in Connecticut prisons.

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