How does the return of Mary Warren intensify John's moral dilemma?

Read the excerpt from act 1, scene 3, of julius caesar. cassius. am i not stayed for? tell me. cinna. yes, you are. o cassius, if you could but win the noble brutus to our party— cassius. be you content. good cinna, take this paper and look you lay it in the praetor’s chair, where brutus may but find it. and throw this in at his window. set this up with wax upon old brutus’ statue. all this done, repair to pompey’s porch, where you shall find us. is decius brutus and trebonius there? cinna. all but metellus cimber, and he’s gone to seek you at your house. well, i will hie, and so bestow these papers as you bade me. cassius. that done, repair to pompey’s theatre. what is cassius’s motivation for sending brutus the letter? cassius wants to make sure that cinna is on his side. cassius wants to reassure cinna that brutus will follow them. cassius wants to sway brutus to kill caesar. cassius wants to alert brutus about the conspiracy against him.