Who was it that wrote the details of the conspirator's plan to assassinate Caesar and delivered it through a man while caesar was heading to the auditorium? Was it one of the conspirators who defected? Why delivered it in such a roundabout manner that has a low chance of actually being read by caesar? Why not hand it in person? Was he afraid that it would backfire on him if his identity was known? But why risk it in the first place? Perhaps it wasn't one of the conspirators but a third party who have leads on the opposition party and wanted to help Caesar anonymously? Too many questions and no answer .
One Roman source, Plutarch's Life of Julius Caesar, identifies this person as possibly being Artemidorus of Knidos and goes into detail:
Furthermore, Artemidorus, a Cnidian by birth, a teacher of Greek philosophy, and on this account brought into intimacy with some of the followers of Brutus, so that he also knew most of what they were doing, came bringing to Caesar in a small roll the disclosures which he was going to make; but seeing that Caesar took all such rolls and handed them to his attendants, he came quite near, and said: "Read this, Caesar, by thyself, and speedily; for it contains matters of importance and of concern to thee." Accordingly, Caesar took the roll and would have read it, but was prevented by the multitude of people who engaged his attention, although he set out to do so many times, and holding in his hand and retaining that roll alone, he passed on into the senate. Some, however, say that another person gave him this roll, and that Artemidorus did not get to him at all, but was crowded away all along the route.
(Julius Caesar 65)
Another, Appian's The Civil Wars, puts Artemidorus on the scene of Caesar's death but does not identify him as the messenger:
While Caesar was actually being borne to the Senate one of his intimates, who had learned of the conspiracy, ran to his house to tell what he knew. When he arrived there and found only Calpurnia he merely said that he wanted to speak to Caesar about urgent business, and then waited for him to come back from the Senate, because he did not know all the particulars of the affair. Meantime Artemidorus, whose hospitality Caesar had enjoyed at Cnidus, ran to the Senate and found him already in the death-throes. A tablet informing him of the conspiracy was put into Caesar's hand by another person while he was sacrificing in front of the senate-house, but he went in immediately and it was found in his hand after his death
(The Civil Wars 2:116)
Cassius Dio and Suetonius, two other Roman sources for Caesar's death, do not go into any detail about the identity of the messenger.