Originally, Manheim was assigned by CIA field director Alexander Conklin to find Jason Bourne and kill him. He was one of the three assassins sent along with Castel and The Professor. Near the end of the movie after Castel and the Professor were killed, Manheim is reassigned by order of CIA Deputy Director Ward Abbott to kill Conklin because of Conklin's failure to apprehend Bourne. Manheim succeeds in this assignment after stalking Conklin to an alleyway and shooting him dead.
Manheim's fate is unknown, as he was the only one of the three assets that Bourne didn't kill, though in The Bourne Supremacy, former Treadstone operative Jarda tells Bourne that they are the last two Treadstone agents, implying that Manheim died of some other cause during the span between Identity and Supremacy.