ISIS leader Abu Bakr al-Baghdadi and al-Qaida leader Ayman al-Zawahiri both have spent considerable periods of time in prison.

Further, one in three terrorists released from prison returns to violent jihad.

These facts should give pause to U.S. authorities, because as many as 100 people convicted of terror-related offenses in U.S. prisons are scheduled to be released in the next four years, warns Patrick Dunleavy, former deputy inspector general for New York State Department of Corrections, writing for the Investigative Project on Terrorism.

Dunleavy writes that "while Islamic terrorist organizations have rapidly changed in their recruitment and tactical methodologies overall, the U.S. has not adapted to countering the evolving threat."

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He noted that amid a vigorous debate over whether to treat terrorists as criminals or as enemy combatants, a "reasonable consensus among the military and the judicial branches is building for the use of both designations."

But there are significant changes in policy and practice toward Islamic terrorists that still must be made, he said.

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One is that with as many as 500 terrorists now in custody and more to come, prisons must change how they handle jihadists.

"Terrorists go into prison much the same way as the burglar, the drug dealer, or the pedophile. They are housed and fed in existing correctional facilities with common criminals," Dunleavy pointed out. "No mandatory rehabilitation or de-radicalization programs exist for convicted Islamic terrorists. And when they are released, there is no specialized supervisory program applied to monitor their employment or whereabouts."

Dunleavy said developing registration lists of convicted terrorists, which has been successfully used with sex offenders, would assist local authorities.

Also, he said, a terrorist prisoner's security classification must not be downgraded simply because he has exhibited good behavior.

"American Taliban" John Walker Lindh, for example, will be released from prison in two years.

Baghdadi's case also makes the point.

U.S. Forces in Iraq arrested him near Fallujah in 2004 and detained him at the Abu Ghraib and Camp Bucca detention centers as a "civilian internee."

In December 2004, the leader of ISIS was released as a "low level prisoner."

No evidence Gitmo causes terror

Dunleavy also calls for the establishment of uniform security standards for imprisoned terrorists in the federal, state and local correctional facilities.

He noted that the alleged "dirty bomber," Jose Padilla, who was "radicalized" in a Florida prison, is scheduled to be released in eight years.

"Who will be the parole officers assigned to supervise him and will those officers be afforded any specialized training before that happens?" Dunleavy asked.

He said that in some cases, specialized facilities such as Guantanamo are necessary in dealing with enemy combatants and other committed jihadists.

"No anecdotal evidence has been presented showing them to be a recruitment tool for ISIS or al-Qaida," he said. "That is like saying that Alcatraz was responsible for the increase in violent crime."

Dunleavy concluded with some sobering facts.

The number of people arrested in the U.S. for terrorism-related crimes nearly tripled in 2015. In that year, FBI Director James Comey testified, more than 200 people traveled overseas from the United States to fight alongside ISIS or al-Qaida related groups in the Middle East and North Africa.

Comey said last year that his agents still had 1,000 open cases related to ISIS, and within the next few years, there may be a "terrorist diaspora" of ISIS fighters leaving the battlefield of Syria and returning to their home countries.

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