This is like, probably the single biggest unresolved casualty of Legacy's sudden cancellation: what in the world was going on with Sia's uncle, Hogrum Chalk? Why was he feeding Krayt information? Why was he pushing Roan to go full Omega Red? Was he actually a Sith stooge, or was he trying to remove Roan from the equation because he blamed him for his sister's death, or was something weirder going on? Does he plug into a charger when he sleeps? And why is his surname Chalk, anyway?
From what John and Jan said on here, it seems like it's definitely due to anger over his sister's death. He wanted Roan finished and Marasiah to ascend.
It's his sister. I doubt Jan & John would have explicitly revealed that even if they had been given more time and space --- the hints are strong enough that it's better storytelling to not spell it out, and to let him get away without any consequences. He blamed Roan for her death, but he loved Sia and wanted the best for her because he saw so much of his sister in her. Spoiler Wish the rug hadn't been pulled out and that he and Havok had had more time to appear in the series before the endgame, so that their development into major major players could have felt a bit more natural and not so sudden.