Evelina Mendoza was an undercover DEA agent. Her DEA handler was Grant Davidson. Mendoza was killed on a bus because she was carrying a secret chip, which was thought to be in her backpack, but was actually implanted in her hand. Evelina Mendoza had been investigating the East Coast faction of a Nicaraguan drug cartel that had recently become aware of The Pattern. Mendoza requested extraction from the operation, which had involved the implantation of a high-tech microchip in the palm of her hand. She was riding a midtown-Boston commuter bus at 8:14 AM when a fellow passenger released an amber contaminant, solidifying the air in the bus and killing everyone inside.
The Fringe Division, upon investigating the apparent terrorist attack, found that while she had originally had a backpack with her, it had gone missing after the attack. Phillip Broyles stated that Mendoza was an exemplary agent, and noted that the attacker(s) may have been interested in whatever Mendoza was carrying.
While identifying her body, Grant Davidson removed an amber-colored microchip from her hand. The identity of Mendoza's killer -- Matthew Ziegler -- was eventually discovered. ("The Ghost Network")