Following the conclusion of the Clone Wars, a devastating massacre took place at Holowan Laboratories. The story goes that the droids were created as part of a clandestine Imperial initiative known as Project Phlutdroid. The initial IG-88 assassin droid transferred its programming to the other three assassin droids. A group of five identical droids, due in part to their faulty programming, murdered their creators and fled their laboratories and escaped into the galaxy.
In the aftermath of the massacre, IG-88B's underdeveloped identity manifested as an obsession with hunting and killing. He played his assigned role by becoming a bounty hunter to divert attention from IG-88A, who was enacting a scheme to overthrow organic life.
The massacre at Holowan Laboratories, while not explicitly named, was first referenced in current canon within the mobile card game Star Wars: Force Collection, which debuted in 2013. Despite Force Collection's launch preceding the Star Wars canon reset of 2014, Lucasfilm Story Group member Leland Chee verified that the game was consistently updated to align with canon. The event was first identified specifically as a massacre in the 2018 reference book Star Wars: The Complete Visual Dictionary, New Edition, authored by Pablo Hidalgo and David West Reynolds.
The IG-88B card featured in Force Collection and the 2016 magazine Star Wars Helmet Collection 2 confirmed the involvement of four identical droids, specifically IG-88 assassin droids, in the massacre. Later, the 2018 publication The Complete Visual Dictionary, New Edition revised this number, stating that five identical droids were involved.
The Holowan Massacre has its roots in the Star Wars Legends continuity. Its initial mention occurred in Galaxy Guide 3: The Empire Strikes Back, a 1989 supplement penned by Michael Stern for West End Games' Star Wars: The Roleplaying Game. The massacre was first depicted in the 1996 short story "Therefore I Am: The Tale of IG-88," written by Kevin J. Anderson and included in Tales of the Bounty Hunters. This version involved four IG-88 assassin droids, IG-88A, IG-88B, IG-88C, IG-88D, and one IG-72.