What is said and done in Act V that supports the comment that Brutus's and Cassius's defeats are revenge for Caesar's murder?Shakespeare's Julus...

In Act V, Brutus has refused to listen to Cassius who
urges Brutus to let their troops wait for those of the triumvirate rather than marching
to Philippi.  Excited by the appearance of the troops of Brutus, Antony exclaims in
Scene 1,

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In your bad strokes, Brutus, you give good
words.

Witness the hole you made in Caesar's
heart,

Crying “Long live! Hail, Caesar!” 
(5.1.31-33)

Brutus and
Cassius say farewell to each other, for they vow not to be taken
alive.

But
this same day 
Must end that work the ides of March begun. 
And
whether we shall meet again I know not. 
Therefore our everlasting farewell
take.
For ever, and for ever, farewell, Cassius! 
If we do meet
again, why, we shall smile; 
If not, why then this parting was well made.
(5.1.122-128)

Omens are seen
by the once skeptical Cassius; then, in Scene 3 Cassius is defeated and he has Pandarus
hold the same sword that struck Caesar as Cassius runs on it.  Later, Brutus discovers
that his friend Cassius is dead and he exclaims,

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O Julius Caesar, thou art might
yet!

Thy spirit walks abroad, and turns our
swords

In our own proper entrails
(5.3.105-107)

Then,
in the final scene, Brutus, too, meets with defeat and kills himself, calling upon
Caesar as he tells his ghost that he did not kill him as willingly as he slays
himself:

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Farewell, good
Strato.

Caesar--now be stil:

I
kill'd not you with half so good a will
(5.5.55-57)

With the 
presence of Caesar's ghost lurking over Brutus, the noble Brutus now sense tremendous
guilt for slaying Julius Caesar, for now all his efforts have fallen apart, thus giving
way to a crueler reign than ever was that of Julius Caesar.