The BBC World Service documentary American Mercenaries : Killing in Yemen is definitely worth a watch. Kind of surprised that it's not been mentioned on this thread yet.
The documentary details how a supposedly 'counter-terrorism' force, including a mercenary company comprised of US mercenaries and lead by an Israeli assassinated targets that were not terrorists, including the 18 year old son of a human rights lawyer etc. The assassinations were initially blamed on ISIS. This was allegedly done on behalf of the UAE government to eliminate political figures they didn't like, and possibly with the knowledge of the CIA. It is also alleged in the film that the supposedly 'counter-terrorist' force also enlisted the help of arrested members of Al Qaeda, including a leading AQ member who was involved in the attack on the USS Cole, killing 17 US Navy sailors and wounding 39 in 2000. The mercenary company (by the name of Spear Operations) also trained Yemenis to carry out the attacks. These operations are also very possibly ongoing aswell.
As I say, it's a BBC documentary and it is available on YouTube, though you have to sign in to watch it.