Some will undoubtedly use this news to make the argument that Guantanamo Bay should remain open, that it should be increasingly used to house the current crop of jihadist terrorists and that no further inmates should be released.
No one is more outraged than me, a counter-extremism specialist, by the reports that a former Guantanamo prisoner joined ISIS and carried out this attack. But keeping the prison and expanding it would not be in the best interests of US or European security.
While military prisons were designed to prevent deaths in war and to speed up the conclusion of conflict, it is clearer now than ever that they do not adequately address the global jihadist insurgency we have faced over the last 15 years.
After Harith was suspected of having links to al Qaeda and the Taliban in 2002, he was taken into American military custody and shipped off to Guantanamo Bay without trial.
Such extrajudicial methods came at the expense of the rule of law and the traditional criminal justice system to prosecute Harith for terrorism-related offenses. It means he was never proven to be a terrorist. It also means we immediately undermined a key aspect of our democracy: a ready-made, values-based alternative narrative to extremism.
The approach of Guantanamo Bay is entirely designed to punish inmates and to gather intelligence. That has notoriously involved the use of torture, including waterboarding, electric shocks, sexual humiliation and sleep deprivation.
While some claim that such an approach has prevented terrorist attacks -- indeed, it is another controversial approach to counterterrorism that the President seems to think of value -- it is also clear it has led to false testimony and has wasted considerable military and security resources, not to mention the illegality and immorality of war-on-terror-era torture.
Moreover, and specific to Harith, it seems he was one of the many recipients of millions of pounds in compensation doled out by the British government in 2010 because of alleged British complicity in torture.
Because of Britain's collective failure to balance national security with civil liberties, a significant amount of money has inevitably ended up in the hands of our enemies.
This torture may have also fed Harith's worldview that he was a victim in a global war against Islam and exacerbated his radicalization.
Whichever way you look at it, torture is an expensive mistake and not one to return to in any situation. It is a small mercy that Trump has deferred to Defense Secretary James Mattis on this point, and we should ensure Guantanamo Bay does not take us back to this era.
Perhaps the biggest issue with Guantanamo Bay is that no time is devoted to deradicalizing inmates. This means that Harith's ideological support for Salafi jihadism
was left unchecked. Given that the ideology that underpins both al Qaeda and ISIS is Salafi jihadism, it is entirely to be expected that previous supporters of al Qaeda may find renewed vigor in their beliefs once ISIS declared its so-called caliphate and feel ideologically obliged to join up as foreign fighters.
It is not so much that Harith was lying in wait for a decade; rather that without ideological refutation and personal rehabilitation, ISIS was the next logical step for him.
Prison systems around the world are starting to adapt to their role in counter-extremism and are now assessing ideological commitment and deradicalizing inmates as part of a broader rehabilitative approach. This will keep our societies safer in the long term by reducing recidivism rates among terrorists. A return to Guantanamo Bay policies without deradicalization will put that in jeopardy.
Extending the use of Guantanamo Bay and torturing suspected terrorists might sound like tough talking on terrorism. But whichever way you look at, it is a stupid move with dire consequences.
The killing of Iraqi civilians and military personnel could have been avoided had we realized this sooner. Instead, the West should pursue a counterterrorism approach that maintains the moral high ground by being consistent with human rights norms and get smart on Salafi jihadi ideology and the wider Islamist narrative.