The event known as either the Holowan Massacre or the Holowan Disaster transpired on the planet Halowan at some point prior to 15 BBY. This incident resulted in the death of numerous scientists and security personnel stationed at the Holowan Laboratories, all due to the actions of the assassin droid IG-88. Upon initial activation, IG-88 murdered those who had created him. Following this, he reprogrammed and activated other IG-series droids. Then, in conjunction with IG-72, he systematically eliminated all personnel within the laboratory complex. After confirming the demise of every detectable employee, the droids fled the planet, setting course for Mechis III to initiate their plans concerning the galaxy.