What is the Old Man's motive in murdering the boy? (Purgatory)

The murdering might inherit from generation to generation. He also believes that by killing his son, he helps his mother get released from purgatory. Hence, the Old Man's motive in murdering the Boy is to break endless cycle of violence.

from: "the tragedy of julius caesar by william shakespeare: act 1 "

the correct answer is:

act 1 opens with the forum in celebration and ends with it in chaos.