Please cite evidence(s) or experiences in Julius Caesar that served to convince Brutus that he was wrong to have killed Caesar.

The question of whether Brutus ever does come to the
realization that he was wrong to have killed Caesar is never fully addressed in the text
of Shakespeare's Julius Caesar. That Brutus realizes the murder of
Caesar was a mistake becomes clear in Act IV, scene iii and Act V, scene iv when he
sees, and reports seeing, the Ghost of Caesar, but being mistaken can take any number of
meanings: a mistaken time, a mistaken group of people; a mistaken method,
etc.

Brutus certainly knows when he sees Caesar's Ghost for
the first time in his tent, in the latter half of Act IV, scene iii, with the promise
that they would meet again at Philippi, that the end of the deed begun on the Ides of
March will be his own ultimate defeat and his own death. Earlier in Act IV, scene iii he
cautions Cassius that they slew Caesar because he was "supporting robbers," so they must
themselves now not become corrupt and take "base bribes." In this Act Brutus is still
determined that they acted as honest citizens who wished to stop a corrupt train of
bribe takers, countenanced by Caesar, that defiled the
Republic.

There are several opinions about the meaning of
Caesar's Ghost calling itself Brutus's "evil spirit" ("Thy evil spirit, Brutus"). One
logical interpretation is that Caesar is asserting that he will have triumph over
Brutus, sort of like the contemporary movie quote, "I'm your worst nightmare," which we
all understand to be a direct threat to the hearer.

Here,
with the ghostly visitation, is where Brutus must certainly begin to entertain the idea
that some error of some sort was made because his only response is to agree that if they
must meet again at Philippi, then they will meet again at Philippi. His next response,
after the Ghost has faded, is to say that now that he has nerve back, he would converse
with the Ghost further. It may have been in this nonexistant conversation that we might
have learned more about Brutus's thoughts.

It is in Act V,
scene iv after seeing Caesar at the battlefield in Philippi that Brutus bows to the
comprehension that he acted wrongly, but it still isn't clear whether he is convinced
that is was wrong because his beliefs were mistaken or wrong because Caesar was too
powerful to go unavenged or wrong for some other reason: The reason for Brutus's
acquiescence to the wrong action is never made
clear.

Brutus's last action and last words do make clear
that he recognizes that Caesar has avenged himself through the opposing
forces:

"O
Julius Caesar, thou art mighty yet!
Thy spirit walks abroad and turns our
swords
In our own proper entrails." (Act V, scene
iii)

It is also clear that
Brutus dies in humility with enlightenment of some sort about the mistake he has made in
murdering Caesar: "Caesar, now be still:/ I kill'd not thee with half so good a will"
(Act v, scene v). But there is no textual evidence to show whether he believes he was
philosophically wrong about "supporting robbers;" morally wrong to think that
assassination was the right means for removing a corrupt government; intellectually
wrong in his definition and assessment of corruption; or personally wrong by being
deceived by the other individuals in the assassination plot.