Dr. Simon Boyd is a scientist who, after his fiancee was paralyzed and eventually died because of the Baghdad Bombing, devoted his life to avenging her.
He and his fiancee, Dolea, were in Baghdad but he took a trip to Jordan. When he returned, Baghdad had been bombed and his fiancee was in a coma. Fifteen years later, she died, and he took a job at a neurotoxin facility to prepare for getting vengeance.
On his way into work, he cut the server wires that would stop an outside source from hacking in. He then locked the building down and filled a room with sarin gas, with a scientist in a suit trapped inside. He set the scientist's suit oxygen to minimum and then sent an email that if POTUS is not on television in 90 minutes revealing the truth, someone will die.
Time is up, and he killed the scientist. He then sent another email, this time with 60 minutes. Walter O'Brien, who had snuck into the building and knew Boyd is the hacker, claimed to be a SWAT Recon Scout. However, Boyd turned and saw on the screens that Cabe was evacuating the building, and manually released the gas. Walter ordered Sylvester Dodd open the door and revealed his part in the Baghdad Bombing. Boyd said that the world will now know how Dolea, his fiancee, suffered, and then he will shoot Walter outside.
He lead Walter at gunpoint to the door, with Walter begging him the whole time not to kill any more people, not to let anyone else die because of Baghdad. Right before they hit the door, Walter disarmed him, cut the server wires he repaired earlier, and escaped right before the front door shut. Boyd began shooting at the bulletproof door, all while sarin gas filled the room and Walter pleaded with Boyd to put down the gun and Walter will find a way to get him out. Boyd, however, dies of the gas.
Boyd loved his fiancee enough that after her death, he embarked on months of planning for a suicide mission in order for the truth of her death to be revealed, as well as all the people trapped inside to die as she did. Even when offered a chance out by Walter O'Brien, he kept shooting even though there was no chance of him killing Walter.
His death would haunt Walter as another death due to Baghdad, and be yet another blow that would lead to his reckless behavior that nearly cost him his life.