"I remember bits and pieces. We were...curious. We tricked Mother Aughra into leaving the Crystal with us so we could experiment on it, and it went wrong." In the initial confusion one of the Skeksis killed a Mystic, and that was how they learned that they couldn't hurt their light halves without killing themselves.

While he didn't remember the murderer, skekGra has some suspects. He thinks it was skekSo who broke the Crystal and caused the Darkening in the first place. While most Skeksis weren't always as bad as they became some, like skekNa and skekSil, were always evil, the only difference between the two that skekNa never truly hid it. The two despised each other, of course.