"There is a network that steers them once they are out of prison through a series of proving grounds until they end up in Yemen," said Patrick Dunleavy, a former deputy inspector general of the New York State prison system.

Pictured here, Attica Correctional Facility. As many as three dozen criminals who converted to...

Pictured here, Attica Correctional Facility. As many as three dozen criminals who converted to Islam in American prisons and later moved to Yemen could pose a "significant threat" to the US, according to a report on al Qaeda from the Senate Foreign Relations Committee to be released Wednesday. The prison converts were believed to be primarily from the New York state prison system.

(Newscom)

"Our informants and electronic intercepts indicated they go through what is called 'underground tactical training' when they get to Yemen," said Dunleavy.

Federal agents broke up a plot in August, 2005 to attack Jewish sites in Los Angeles that they say was hatched inside Folsom Prison by militant Black Muslims who had sworn allegiance to a violent jihad.