In the year 3643 BBY, as the Cold War neared its conclusion between the Galactic Republic and the Sith Empire, Tarnis, a Sith Lord operating in secret, orchestrated the abduction of his Republic scientist persona, Eli Tarnis, with the assistance of the Black Sun crime organization. Utilizing Tarnis's acquired knowledge, the criminal Zeer and his associates successfully infiltrated the Senate Building located on Coruscant, the Republic's capital, and extracted the doctor from within the heavily fortified structure. While Zeer and his crew created a diversion by barricading themselves within Docking Bay 84 of the adjacent Coruscant Spaceport, Tarnis made his escape to the territory of his allies, the paramilitary group known as the Justicars' Brigade, where he continued his machinations to obtain the Planet Prison superweapon.
Back in 3643 BBY, amidst the ongoing Cold War that pitted the Galactic Republic against the Sith Empire, the Jedi Council detected a disturbance through the Force emanating from the Republic's capital, Coruscant. Consequently, they dispatched Jedi Master Bela Kiwiiks and her Padawan, Kira Carsen, to investigate the matter. Kiwiiks verified the presence of a dark presence on the capital world, unaware that its origin was actually the Sith Lord Tarnis, who was masquerading as Eli Tarnis, a Republic scientist involved in the Republic superweapon initiative. Recognizing that his position was at risk, Tarnis reached out to the Migrant Merchants' Guild and the Black Sun criminal organizations, arranging for the theft of the design specifications for his project, the Planet Prison superweapon, with the intention of diverting any potential suspicions away from himself.
When a young Jedi Knight, previously apprenticed to Jedi Master Orgus Din, was sent to retrieve the stolen files from the criminals located within the Old Galactic Market sector, Tarnis made contact with Salarr, the leader of Black Sun. In exchange for weaponry and technology originating from the Empire, Tarnis requested that Black Sun stage his "kidnapping" to facilitate his escape from the Senate Building undetected, allowing him to proceed with his schemes to acquire the Planet Prison.
Leveraging the confidential data provided by Tarnis, a squad of Black Sun criminals, led by the Human Zeer, successfully breached the security of the Senate Building. They subdued the Coruscant Security Force officers and Republic Military personnel responsible for guarding the premises. Tarnis was swiftly extracted by Zeer's team before any alarms could be activated.
However, the Security forces, alongside agents from the Republic Strategic Information Service, the Republic's intelligence division, quickly discovered Tarnis's disappearance. Agent Galen of the SIS promptly instructed Kira Carsen to lead a contingent of Coruscant Security officers toward the nearby Coruscant Spaceport in pursuit of the kidnappers.
As planned, Tarnis departed from Zeer's group at the Senate Plaza and boarded an air taxi destined for Black Sun territory, but he rerouted the taxi to Justicar territory, an area of Coruscant under the control of the Imperial-sympathizing paramilitary organization known as the Justicars' Brigade, where he pressed forward with his plans to secure the Planet Prison itself. Zeer and his accomplices fortified their position within Docking Bay 84 of the spaceport, intending to create a distraction. Nevertheless, Carsen and the CSF officers eventually broke through the criminals' defenses with the assistance of the Jedi Knight who had been dispatched to recover the stolen design files. The Knight was subsequently assigned a mission to rescue Tarnis from Black Sun territory, but Tarnis's deception and true identity were exposed during the rescue attempt.
The kidnapping of Doctor Tarnis is initially mentioned in Star Wars: The Old Republic, a video game developed by BioWare and published by LucasArts in 2011, specifically at the conclusion of the Jedi Knight class mission titled "Stolen Secrets." The subsequent mission, "Kidnapped," revolves around the pursuit of Tarnis's captors, but it isn't until the following mission, "The Rescue," that the revelation of Tarnis's orchestration of his own kidnapping is revealed.