When radicalised terror offenders are released from prison, how should they be dealt with?

Two recent attacks in London have brought the question into sharp focus because both involved extremist offenders carrying out knife attacks despite being on the radar of security services.

Sudesh Amman, 20, carried out the Streatham attack last month only 10 days after his release from jail. It was a case that reverberated across Europe, where other offenders will soon be freed.

The UK quickly passed legislation to block the automatic early release of convicted terror offenders. Other European countries are grappling with the same balance between security and civil liberties. For terror offenders, a second chance comes with many strings attached.

How many terror offenders are there?

Hundreds will be released from European prisons within the next few years, figures suggest. Europol, the EU's law enforcement arm, gives an idea of the numbers.

From 2016 to 2018, Spain had the most court cases for terror offences (343) in the EU, followed by the UK (329), France (327) and Belgium (301).

In 2018, 61% of verdicts for those cases in EU states were classed as "jihadist terror offences". This verdict trend, Europol said, started in 2015 - a year after the Islamic State (IS) group declared its caliphate in the Middle East.

Radicalised by IS, jihadists carried out a series of atrocities. The November Paris attacks in 2015 claimed 131 lives and the Nice lorry attacker murdered 86 people in July 2016.

Terror offenders do not stay behind bars forever - a point underlined by Globsec, a think tank. Of 199 individuals arrested for terror offences in 2015, 57% would be released by 2023, it said. Their offences range from planning attacks and membership of a terrorist group to financing terrorism.

In France alone, around 45 of the more than 500 terror offenders in jail are expected to be released this year. In the UK, the number is 50, in Sweden it is zero.

Most European countries run or fund rehabilitation programmes. These are mostly small-scale programmes focused on a limited number of offenders. They can be mandatory or voluntary.

Some aim to change the behaviour of offenders - which is known as disengagement; others seek to overhaul their ideological outlook - called deradicalisation. The process typically starts in prison, where inmates are considered vulnerable to radicalisation.

How Germany tries to deradicalise its offenders

Violence Prevention Network (VPN) is just one of the numerous civil society groups dealing with the deradicalisation of extremist offenders in Germany.

When it was founded in 2001, VPN dealt with few serious terror convicts. Young offenders at risk of right-wing extremism were its target group.

That changed in the mid-2010s, when Islamist fighters started returning from war zones, bringing their extremist views into prison with them.

"These individuals are so dangerous, you can't train them in a group," Cornelia Lotthammer, a spokeswoman for the VPN, told the BBC. "There's always a risk that the group will be manipulated."

These hard cases require two-on-one training for as long as it takes, often mandated by court order. Even then, some simply refuse to yield. Funded by the German government, VPN also offers a voluntary programme for less serious offenders.

Its guiding method of "education of responsibility" involves careful detective work. A key element is developing an understanding of the offender's biography, from fond childhood memories to their acts of violence.

"We try to detect crucial points in their biography, when they took the wrong road," Ms Lotthammer said.

In the post-prison phase, it is up to offenders to "choose another way". A combination of counselling, vocational training and family support for up to a year is supposed to ensure they do so.

How France tries to chip away at extremist ideology

Offenders radicalised in prison have been a particularly prickly thorn in France's side.

The Charlie Hebdo and Paris attacks of 2015 involved extremists who had served time in jail. Now, more than 1,000 current inmates have been flagged as radicalised.

To dissuade them from following the same violent path, France has funded a dizzying array of deradicalisation programmes. They have been criticised for their cost, unclear results and stigmatisation of Muslims.

With past mistakes looming large, Prime Minister Edouard Philippe announced a new counter-terrorism plan in 2018.

Under the plan, radicalised offenders are assessed in specialist units of high-security prisons and segregated in separate wings if necessary. This is not optional, but some offenders are unco-operative.

By talking to inmates one-on-one, social workers aim to chip away at their extremist ideology, dismantling it bit by bit.

After prison, a court may send an offender to one of France's four new deradicalisation centres in Paris, Marseille, Lille and Lyon. At these centres, treatment continues under the supervision of tutors, psychologists and religious advisers (imams).

France's first rehabilitation centre was deemed a failure and shuttered in 2017, and few of those admitted were considered dangerous extremists.

But Coralie Tchina of France's Ministry of Justice says they have since evolved. "We take care of Islamic terrorists, but also radicalised people with convictions for lesser crimes."

"For now, it's kind of working," she told the BBC.

How the Dutch have beefed up probation

The Netherlands has not suffered terror attacks on the scale of its European neighbours, yet Dutch authorities know they cannot afford to be complacent.

Gokmen Tanis has admitted shooting dead four people on a tram in Utrecht and is accused of murder with a terrorist motive.

A known offender awaiting trial for rape, Gokmen Tanis showed no signs of extremism before the attack, prosecutors said. Anyone flagged as radicalised in the Netherlands can be referred to TER (Terrorists, Extremists and Radicals).

Launched in 2012, TER sees itself as a beefed-up version of probation rather than a deradicalisation programme.

"It is about probation work - just like with other target groups - that is supplemented with specific measures," Stephanie van Erve, a spokeswoman for the Dutch Probation Service (DPS), told the BBC.

As part of their parole conditions, offenders are supervised by TER and, in some cases, tracked with GPS technology by intelligence services. With the support of Islamic theologians, TER staff promote behavioural and ideological change.

What are other European countries doing?

Many have programmes based on a two-step strategy: intervention in prison and after-care outside prison. Denmark, for example, separates extremist offenders and requires them to participate in its Back on Track programme before release.

The Belgian government similarly views prison as "a potential breeding ground for radicalisation". A voluntary programme geared towards disengagement - behavioural change - has been developed in Belgium. Last year, 27 inmates were selected to take part in the nine-month programme, named Césure.

The Spanish model runs voluntary deradicalisation programmes in a handful of prisons. An EU report says the plan encourages violent radicals to "address religion from a rational point of view" and learn democratic values. As of 2018, none of its 23 participants had renounced their extremist ideology, a report by El Periódico said.

Rehabilitation programmes: a model for success?

No-one knows for sure. The results of these programmes are not well understood for two main reasons.

First it is difficult to evaluate their success scientifically because legal, ethical and security concerns place restrictions on doing so. But also many of these programmes are in their infancy, so no proper case studies or data exist and there is no consensus on what constitutes best practice.

There are reasons to be optimistic, though. Of the 189 offenders supervised by the Dutch programme, a study found that only eight showed signs of recidivism - a tendency to reoffend - between 2012 and 2018. Of the most serious terror offenders supervised by VPN, none has relapsed.

That's why Ms Lotthammer was so surprised by the London attack in January.

"What amazes me is that the first thing [Sudesh Amman] thought to do after leaving prison was attack people under the ISIS flag," she said.

Scotland Yard's counter-terrorism chief Neil Basu suggested Amman was beyond rehabilitation. It is not clear what support he received in prison. But even if more could have been done, no programme has a tried and tested recipe for success.

To have a chance, they need to be "well-staffed with well-trained personnel and adequate methods and tools available", Dr Daniel Koehler, director of the German Institute on Radicalization and De-Radicalization Studies (GIRDS), told the BBC.

"In most countries, this is not the case so that these programmes are really not reaching their potential impact," Dr Koehler said.