The treatment of Yazidis, otherwise known as genocide.


https://www.nazandbegikhani.com/info/why-isis-s-treatment-of-yazidi-women-must-be-treated-as-genocide-630.html
The above is an illustration of what wannabe returning jihadis are capable of.

Incarcerate,punish if required, free only after being subjected to successful intensive de radicalization programs. Far better such a process is carried out in their country of capture, where more robust measures exist to deal with them.