Cassius evidence

Spark notes -
Cassius -  A talented general and longtime acquaintance of Caesar. Cassius dislikes the fact that Caesar has become godlike in the eyes of the Romans. He slyly leads Brutus to believe that Caesar has become too powerful and must die, finally converting Brutus to his cause by sending him forged letters claiming that the Roman people support the death of Caesar. Impulsive and unscrupulous, Cassius harbors no illusions about the way the political world works. A shrewd opportunist, he proves successful but lacks integrity.

I would like to use the letters as evidence against Cassius. This way we can stay true to the story and also have more layers in the piece.