Unbeknownst to his fellow Assassins, Steve was actually a mole acting on behalf of the Templars, informing his superiors to all the discoveries of his cell, including information on the Scepter of Aset.
In 2012, while Hawk relived the memories of Numa Al'Khamsin, a serious incident occurred which caused Hawk to fall into a coma and he was taken to the hospital. When he was alone with Jonathan, Steve saw the chance to kill the Assassin by removing his oxygen mask.
However, when he left the room, Steve was confronted by Stella and Nancy, who found out about Steve's secret defection to the Templar cause. Although he was held at gunpoint by Nancy, Steve remained calm and tried to explain his presence at the hospital. His tranquility turned into panic when Jonathan appeared at his side and Steve tried to flee by pushing Nancy aside. Jonathan, however, chased him down and killed him.