As the United States and its coalition partners continue to squeeze ISIS out of its remaining territory in Iraq and Syria, more and more foreign fighters are returning to their home countries. This migration from the battlefield to the hometown is causing great concern among Western counterterrorism authorities. The question on everyone's mind is how long before the returning jihadists unleash an attack on their own countries.

Not very long, according to a new study on terrorism and political violence. Within one year, the study found, and in some cases as little as months, returning fighters attempted a terrorist attack in their home countries. The term researchers used to describe that period was, "Lags in Attack Times of Extremist Returnees (LATER)."

The most effective way to mitigate the threat, authors David Malet and Rachel Hayes say, is to take immediate corrective action when a jihadist returns home. Increased security and a vibrant de-radicalization program can help the returnees peacefully reintegrate to Western society.

This advice is just as important for American prison officials to heed.

Malet, an American University assistant professor in criminology, and Hayes, a Treasury Department employee, examined the cases of 230 Western returning "jihadi foreign fighters between 1980 and 2016."

While some counterterrorism experts believe incarcerating the returning terrorists would deter future action, the study found the opposite is true: "Prison appears to play no role in lag times." While an incarcerated returnee may not be able to physically conduct an attack, he can recruit others and has the ability to plot or coordinate an attack from his prison cell.

So what does happen when terrorists are placed in prison? They try to attract other inmates to their cause. "Every time we put them with the rest of the detainees, they engage in recruitment activities," said Belgian criminologist Valerie LeBrun.

This should come as no surprise as we have outlined in the past and a 2004 report by the U.S. Department of Justice confirmed, "inmates incarcerated for crimes connected to terrorism or inmates who have received overseas religious instruction may possess extra credibility with other inmates, enough to gain a religious following within the prison."

Belgian criminal Benjamin Herman provides a recent example. Jailed for robbery and drugs, he entered prison as a common criminal who claimed to be Catholic, fell under the influence of radical Islamic inmates, and converted to Islam. Before his release in May, authorities were warned about his radicalization, but were unable to stop him. He killed two Liege police officers and a school custodian, while shouting "Allahu Akbar" as he was brought down by a hail of police bullets.

In light of this, it would seem that the simplest solution to preventing prison recruitment would be to isolate the incarcerated terrorists from other inmates.

But the sheer number of inmates jailed for terrorism related crimes makes that difficult. "Never have so many people been arrested on charges related to terrorism, and never have we seen so many of these guys in prison together," said Thomas Renard, counter terrorism expert and senior fellow for Belgium's Egmont Royal Institute for International Relationships.

Great Britain and France have created new prison units for terrorists, but have found that these special arrangements do not eradicate the threat. "Every radical Islamist convict will be released from the correctional facilities some day," Eva Kühne-Hörmann, Germany's Hessian state minister of justice, told the Washington Post.

French authorities acknowledge that "hundreds of inmates, radicalized during the war in Syria and the rise of Islamic State ... will be released from French prisons before the end of next year." The United States is facing a similar situation with the anticipated release in the next two years of as many as 100 inmates convicted of terror related crimes. Among them is John Walker Lindh, captured in 2001 in Afghanistan, fighting against United States coalition forces.

Given these facts, it is disturbing to find that authorities here and in the EU have failed to develop and mandate some sort of de-radicalization program while terrorists are still in prison.

While many of the prison programs help inmates deal with alternatives to violence, none address the radical Islamic ideology which is seen as the cause for much of the terror attacks here and in the European Union. "Nonviolence, not deradicalization, remains the primary goal," Lebrun said.

But some in the Muslim community disagree with that approach. "The prisons are trying to quarantine the virus, but they don't really address the problem, "We need experts in ideology," Brussels imam Ilyas Zarhoni told the Post.

In Great Britain, inmates convicted of terror related crimes have simply refused to attend any de-radicalization program.

Some attorneys in the United States strongly oppose any de-radicalization program that they feel violates the offender's constitutional right to religious freedom. But they ignore the fact that terrorists in prison frequently use that very right to sue prison officials for privileges and easier jail time. Convicted 9/11 conspirator Zacarias Moussaoui wants a wall clock and a digital watch while he serves out six life sentences with the Bureau of Prisons. There isn't a clock in the world big enough for that amount of time.

To better address the problem, we might increase the number of probation officers assigned to monitor released inmates, with specialized training for those responsible for supervising paroled terrorists. Another strategy would be to create a national registry for convicted terrorists similar to what is used for convicted sex offenders.

It we do not address this problem quickly, prisons may easily become conveyor belts for would be jihadists.

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.