Farid Benyettou is a former extremist street preacher who has publicly renounced jihadist ideology.

Once nicknamed the "imam Voltaire" after the high school he left to become a backroom preacher to young Muslims in his Paris neighbourhood, Benyettou has written a book detailing his descent into becoming a propagandist of Islamic extremism.

He is one of those who fear that Europe is not braced to cope with the dozens of terror convicts set to be released by European prisons.

Over the next two years, more than 200 inmates, who largely formed the first wave of jihadis streaming to Syria and Iraq, dreaming of an Islamic caliphate not yet established, will walk free from prison.?

Benyettou views the coming round of prison releases with an apprehension born of firsthand experience.

"You have to understand what happens in the mind of someone who is radicalised. You have to understand this double set of beliefs," he said in an interview with The Associated Press.

In all, about 12,000 Europeans left to fight with the Islamic State group (IS) and al-Qaida; about a third of those are now believed to be home, mostly living freely.

Some are awaiting trial, but most never faced serious charges due to insufficient evidence.  

And many more saw their travel plans thwarted, staying at home to stew.

How much of a threat do these avowed extremists living throughout Europe pose, and how equipped are authorities to handle them?

The response has been, at best, improvised.

Some scholars believe the issues that led to radicalisation need to be addressed or an environment conducive to jihadi violence will continue.  

"The transition phase from prison to after prison is the most challenging aspect of all," says Thomas Renard, Senior Research Fellow at the Egmont Royal Institute for International Relations.

"This is when a person after several years in Syria or Iraq, in a  combat zone, after several years in prison, a highly radicalised and radicalising environment, goes back to the society as a free citizen, that person is extremely vulnerable, vulnerable to fall back into the same dynamic that has led to him or her deciding to leave to Syria or Iraq in the first place," he adds.

Benyettou, now 38, spent four years in prison on terrorism charges, alternating between recruiting fellow inmates to the cause and furiously studying for his degree.

It took years for him to disavow the ideology he once spread so effectively. Now, he says extremism sows only death.

"If I had to do it over again, if I had this view of the world that I have now I wouldn't make the same mistakes. I lost years of my life and still more. There are people who lost their lives in this whole story. It's not just my little youthful digression that I can leave in my past. It's something with serious consequences."

Among the group of young men he once led are Cherif and Said Kouachi, who gunned down 12 people at the offices of the satirical newspaper Charlie Hebdo in 2015.

Another follower blew himself up in Iraq; yet another died in Syria fighting for the Islamic State group.

The cell he once led epitomises the urgent question Europe now faces: Are the terrorism convicts on the verge of freedom like Benyettou, like the Kouachis or somewhere in between?

"These guys who are convicted today or who are awaiting trial will get out one day," Benyettou said.

"And that's the issue, in fact: What kind of preparations will there be for their release?"

Terrorism prison sentences in Europe until very recently averaged about six years, compared with 13 years in the United States, according to Europol data.

Since 2015, sentences have risen, but remain well below US levels.

The Paris prosecutor general recently told Le Monde newspaper that the risk of recidivism is a danger.

Thomas Renard agrees.

"The problem is, we are not really sure how many of them will remain a threat. So that means it will require a constant monitoring," he said.

France, which has been struck repeatedly by IS fighters and sympathisers, will free 57 inmates - about half its current population of terrorism convicts.

In Britain, 25 inmates are due for release - fully three-quarters of its terrorism convicts.

In Belgium, 80 acknowledged foreign fighters already are free and as many as 44 others will be joining them.

In Spain, 21 of 34 returning extremists already were free as of late last year.

And in Bosnia and Kosovo, every jailed foreign fighter will go free.  

In just those countries alone, the total runs to more than 200, according to the AP's count.

And the actual number is undoubtedly higher because not every country releases data - most notably Germany, which had nearly 1,000 residents make jihadi trips but has not released any comprehensive figures on convictions or releases.

The most recent attack blamed on returning foreign fighters was in March 2016, when an Islamic State cell of jihadis set off suicide bombs at the Brussels airport and in the metro.

The overwhelming majority of returning jihadis have not been arrested and have caused no harm.

Once they leave prison, no programmes or policies govern them.

France has applied a range of post-release constraints, ranging from requiring those freed to periodically check in with authorities - as is the case for Benyettou - to perpetual home detention for former prisoners like Kamel Daoudi, who was convicted in a plot to bomb the American embassy in 2005 and has been under house arrest since his 2008 release.

In Bosnia, where all 23 terrorism convicts already are done with their sentences or soon will be, the Justice Ministry said local housing, social workers and employment agencies are notified, but that there's little capacity to do much more.

Britain has limited counselling and monitoring, and offers a voluntary re-integration programme.

Spain theoretically began "re-education and reinsertion" in 2016 in which terrorism inmates are evaluated by their perceived risk level and undergo the appropriate counselling.

But according to the government, only 10 out of the 146 inmates jailed for ties to extremist Islamic groups actually have undergone the much-hyped deradicalisation programme.

The Interior Ministry refused to explain why.

Expelling the extremists is not a realistic remedy: The vast majority of the continent's foreign fighters and sympathisers are purely European, which means they cannot legally be stripped of citizenship or deported.

Those who are legally judged to be dangerous are likely to remain behind bars for years to come: Salah Abdeslam and Mohamed Abrini, both linked to the Islamic State network that attacked Paris and Brussels, have not even come to trial on those charges.

As for Benyettou, he decided to become a nurse after leaving prison in 2009.

But his dreams of becoming a nurse evaporated with the Charlie Hebdo attacks - no one would hire him after learning of his ties to the Kouachi brothers.

So he now is training to be a truck driver.

He is philosophical about yet another dramatic shift in direction.

"Everyone has setbacks in life, plans that don't happen. For me, it's my past," he said.

"You bounce back and try to do something besides falling back on this logic of victimhood, to say 'They'll never want us anyway. They'll never let us dig ourselves out'."

Having a plan - any plan - was crucial to Benyettou leaving extremism behind.

And that's where many fear not just France but all of Europe will fail the next wave of terrorism convicts.