The Soheras Trench Massacre was a component of the Genocide of Mon Calamari. This genocide was commanded by Darth Krayt as retribution against the Mon Calamari for their support of the Galactic Alliance Remnant. Darth Azard, a Quarren Sith Lord, gave the order for this massacre. It was also used to evaluate the capabilities of the Sea Leviathan, a semi-sentient type of Sithspawn. This creature was created by Sith scientist Vul Isen, using the ancient Leviathans from the Hundred-Year Darkness as a template. The creature exterminated all the prisoners held at Imperial Extermination Camp 28, which was situated on Soheras Trench. The Leviathan had been kept dormant there, awaiting its deployment orders. After the complete annihilation of the camp's inmates, Lord Azard and Isen dispatched the Sea Leviathan to hunt down the Mon Calamari Rangers.
This massacre was depicted in Legacy (2006) 32, a comic that came out in 2009. This issue, the first in the Star Wars: Legacy Fight Another Day story arc, was written by John Ostrander and illustrated by Omar Francia.