Oops:
An instructor teaching his militant recruits how to make car bombs accidentally set off explosives in his demonstration Monday, killing 21 of them in a huge blast that alerted authorities to the existence of the rural training camp in an orchard north of Baghdad. Nearly two dozen people were arrested, including wounded insurgents trying to hobble away from the scene.
As the saying goes, those who can't do, teach. It's possible the instructor had no experience with this sort of thing. It's certain, actually, since he (was) alive.
Al Qaeda's OSHA (Osama Suicidal Homicide Administration) is no doubt very upset that ISIS was this sloppy. No wonder al Qaeda Prime took away their secret decoder rings.
I hope it was very painful for all of those SOBs.