Most of the main characters are not "innocent." However, in a sense the common people of Rome are innocent of the political underhandedness that the main characters are engaged in. They are misled constantly by those in power. Most impressively, they are manipulated by Antony at Caesar’s funeral. Antony’s powers of persuasion are evident on the steps, as he turns the people against Brutus and the conspirators. They are misled by Antony’s promise of the gifts in Caesar’s will, which he later withholds.
Caesar himself is also misled by the conspirators, who profess their allegiance to him right up until the assassination. It is Brutus that “hurts” Caesar the most, as he is the last person Caesar would have suspected of treachery.
One could make a case that Cassius misleads Brutus with a little bit of trickery by sending him letters that appear to have been written by several different people. This is part of his plan to convince Brutus to join the conspiracy. However, Brutus probably would have turned against Caesar anyway.