Seems there should be a demon here surrounded by spell-weaverss here. Only found a German video where he kills the warlocks to release him. His release /yell translate to "Prepare to die!". The demon is called "Enslaved Doomguard" with the ID 21963. He also attacks nearby Cabal NPC's as you can see in the video.

https://youtu.be/miHflW-_xcA?t=217
https://youtu.be/Swws76ZCG7Q?t=61
https://youtu.be/WftCLjFrzmE?t=51