Preventing or even minimizing prison radicalization is always a challenge. It's more difficult, however, when we continually fail to vet the chaplains who minister to inmates.

Germany appears to have learned this lesson recently. Authorities there recently discovered that over 85 percent of their Muslim prison chaplains were actually agents of the Turkish government, the Gatestone Institute reports. Those clerics had to be terminated after the Turkish government refused to have them go through security checks, which are required by German law for all prison chaplains. And while the number of foreign-born inmates in German prisons has spiked to nearly 50 percent, the vast majority of those are from Poland, Tunisia, the Czech Republic, and Georgia, not Turkey.

One wonders why the need for the 97 Turkish prison chaplains who were let go.

Germany now has 25 Muslim chaplains. This reduction comes in the light of the increased number of Muslim inmates in their system and the fears of the increased threat of radicalization.

The Muslim chaplains are represented by the Turkish Islamic Union, or DİTİB, which has been under investigation by Germany's Domestic Intelligence agency after it found a connection between Turkish military action in Syria and a rise in persecution of Turkish dissidents. It was also discovered that some DİTİB chaplains were providing names of dissidents to their embassy in Germany.

This is not the type of religious figure you want ministering to a captive audience vulnerable to radicalization.

Authorities both here and in the European Union have known for years the powerful influence a prison chaplain can have on an incarcerated individual.

The right chaplain can help the inmate on the path to rehabilitation and restoration of family ties. The wrong one can be like a wolf in sheep's clothing filling the inmate's mind with a radical ideology that pushes him or her down the road to jihad. Only a thorough vetting of religious clergy and volunteers can reduce that threat.

When I testified before Congress in 2011 on the threat of prison radicalization, I was asked by U.S. Rep. Sheila Jackson Lee, D-Texas, if there was any difference between Islamic radicalization in prison and other types of radicalization such as Christian militants in prison. My answer was succinct, "Foreign country backing and foreign country financing."

While investigating radical Islamic influences in prison, we found several indicators that contributed to the radicalization process. One was foreign born inmates who had already committed terrorist acts. Improperly vetted clergy also play a role, along with foreign funds that came to organizations like the North American Islamic Trust Fund, the Islamic Society of North America (ISNA), the Islamic Development Bank in Saudi Arabia and the Graduate School of Islamic Social Sciences (GSISS).

The GSISS was founded by Taha Jabir Al-Alwani, an Egyptian cleric who worked closely with Palestinian Islamic Jihad operative Sami Al-Arian and helped finance Al-Arian's think tank. Al-Alwani was also investigated for his involvement with the SAAR Foundation, a Saudi-funded organization, based in Herndon, Va., that was suspected of funneling money to terrorist organizations.

Some of that money from these foreign sources were used to pay for overseas travel for Muslim prison chaplains and also literature for the prison libraries that promoted a Salafist/Wahhabi view of Islam.

In 2014, the Federal Bureau of Prisons hired an Egyptian born cleric, Fouad El Bayly, to be a prison chaplain. As president of the Islamic Center in Johnstown, Penn., he publicly called for the death of Ayaan Hirsi Ali, a former Muslim, activist, and writer who was a vocal critic of Islam's subjugation of women. Ali "...has defamed the faith," Bayly said. "... and when you decide to defame it deliberately, the sentence is death."

That revelation prompted U.S. Sen. Charles Grassley, R-Iowa, to request a list of organizations that the Bureau of Prisons (BOP) was using to assist in its background checks of potential religious workers. Grassley was outraged to find ISNA on that list. ISNA's history of ties to the Muslim Brotherhood has been well documented by the Investigative Project on Terrorism.

With blatant incredulity CAIR spokesman Ibrahim Hooper came to ISNA's defense, accusing Grassley of Islamophobia.

"This is an extremely old issue that has been circulated endlessly on anti-Muslim hate sites and it's a bit surprising to see an elected official promoting these kinds of Islamophobic smears," Hooper told FoxNews.com. "(ISNA) is a well-respected Muslim organization that for decades has made positive contributions to our nation, and like any Muslim-American organization they are frequently targeted by scurrilous attacks whose only goal seems to be to demonize and marginalize American Muslims."

In fact, it was federal prosecutors and documented evidence which connected ISNA to the Muslim Brotherhood and Hamas financing. Prosecutors included ISNA among groups and people "who are and/or were members of the US Muslim Brotherhood" during the Hamas-financing trial against the Holy Land Foundation for Relief and Development and five former officials. Bank records admitted into evidence show that ISNA served as a conduit for Holy Land Foundation contributions. Some checks that passed through ISNA accounts were made payable to "the Palestinian Mujahadeen," the original name for the Hamas military wing, prosecutors said.

New York's Majlis Ash-Shura also was on the BOP list. It includes the Islamic Circle of North America (ICNA), an organization with direct ties with Jamaat-e-Islami, a Pakistani-based terrorist group.

ICNA's goals include the establishment of a caliphate, or global Islamic state, its 2010 member handbook said.

ICNA has published literature that describe jihad as a form of worship.

"Groups like ICNA do not promote Islam, but rather Islamism, the linking of politics and religion," said Zuhdi Jasser, founder of the American Islamic Forum for Democracy.

This appears to be what the Turkish prison chaplains were trying to do in German prisons through DİTİB.

Organizations with this type of ideology should not be relied upon to certify potential prison chaplains. It only risks promoting radicalization among the inmates and destabilizing the already fragile prison environment.

IPT Senior Fellow Patrick Dunleavy is the former Deputy Inspector General for New York State Department of Corrections and author of The Fertile Soil of Jihad. He currently teaches a class on terrorism for the United States Military Special Operations School.