The author, C.M.C. Green, portrays the necessity of the murder in Lucan's Book 3.

Lucan created the relationship between Pompey and Caesar, it has been argued, on the pattern of the relationship of Agamemnon and Achilles. Thus it is through an acknowledgment of his Greek literary ancestry that Lucan constructs the opening of his epic. The rivalry between the great leader and the young warrior provides the explosive, psychological beginnings (hae ducibus causae …) of the action of the Bellum Civile, shaping the conflict as one which, while between individuals, remains even less personal than that between Agamemnon and Achilles. Yet, though Achilles threatens, he does not in the end take his men home and abandon Agamemnon. Their personal quarrel is resolved, and thus subordinated to their obligations in the greater battle against the Trojans. Caesar, enraged with Pompey's arrogance, does take his troops home; the Iliadic...