Sien, holding the position of Mine Foreman at the Peragus Mining Facility, was in charge leading up to the Skirmish at Peragus II which occurred in 3951 BBY. When the Jedi Exile, who was running away from Darth Sion, arrived at Peragus on the badly damaged Ebon Hawk, Sien was one of the facility's staff members.
Coorta tried to persuade Sien to sell Meetra Surik to the Exchange for a lucrative bounty when she got to the mining facility. Sien declined, partly because he wanted nothing to do with the Exchange. Furthermore, he was afraid of Jedi, thinking that angry Jedi caused 'big wars' with widespread destruction. Sien's efforts to get Coorta to drop the idea were unsuccessful, and soon after, he overheard Coorta plotting with an HK-50 droid (with a voice disguised as the Maintenance Officer) to hand Surik over to the Exchange. Sien initially thought about reporting these plans to the Administration Officer, but he felt that this would only make things worse.
After discovering more about Coorta's scheme, including what would happen to all of the miners, he thought he could convince the Maintenance Officer to abandon the plot. However, the Officer was unaware of Sien's knowledge. He was recording a log on his datapad titled "Time to take action!" when Coorta attacked him, rendering Sien unconscious. The log continued to record a brief conversation that followed, in which Coorta discussed the specifics of his plan with two accomplices. Realizing that the datapad was still recording, he ordered it to be turned off and sent down the refresher.
It's possible that Sien informed the administration officer after everyone was confined to the dormitories during the emergency lockdown. It is believed that he died due to the toxic fumes that were released into the dormitory level's ventilation system. The logs Sien recorded may have been discovered and examined by Surik as she attempted to piece together the events that had transpired at the mining facility.