This seems … kind of important:

More from the BBC:

The self-styled Islamic State group said two days ago that Abu-Zakariya al-Britani detonated a car bomb at an Iraqi army base in Tal Gaysum, south-west of Mosul.

He had been seized by US forces in Pakistan in 2001, before being sent to Guantanamo.

US interrogators found he provided useful information to them about the Taliban’s methods, and he was released after two years.

… Oops?

That’s why you don’t let people out of Gitmo.

Editor’s note: This post has been updated with an additional tweet.