Matthew Ziegler is an assassin whose overall mission was not revealed. His immediate objective was to recover a high-tech chip from several DEA agents that possessed the chip at one point or another. Ziegler committed mass murder on an early morning commuter bus and assassinated a Federal Law enforcement agent in a crowded train station. He released an amber gas canister on the crowded bus, killing eleven onboard and DEA Agent Evelina Mendoza. The gas caused the nitrogen in the air to solidify, immobilizing and suffocating fellow passengers like 'insects in amber'. Ziegler survived by donning a gas mask. He also collected all of the backpacks as he exited the back of the bus.
Ziegler's superiors were not revealed, but the purpose of his attack on the commuter bus was to gain control of a crystalline disk possessed by Agent Mendoza. An accomplice of Ziegler's, Gerard, spoke only Latin while speaking on the secure communication system they utilized.
Having failed to recover the chip from Mendoza, Ziegler arranged a meeting with her handler, DEA Agent Grant Davidson. During their arranged meeting at the 'South Station' rail terminal, Ziegler assassinated Davidson with a single gunshot to the chest. As he fled with the high-tech chip, FBI Agents Olivia Dunham and Charlie Francis isolated him and tried to arrest him. To avoid arrest, Ziegler committed suicide by stepping in front of a rapidly moving train. ("The Ghost Network")