Who assasinated Caesar?

Cassius Dio wrote that a certain Fannus Caepio instigated a plot against Augustus and said that "[e]ven Murena was reported to be in the conspiracy, whether truly or by way of calumny, since he was immoderate and unrestrained in his outspokenness towards all alike." The men did not turn up for the trial and were convicted in absentia "on the supposition that they intended to flee; and a little later they were slain." Cassius Dio also said that some of Murena's relatives were "most highly honoured by Augustus" but did not intervene to try to save him. He also said that because some of the jury had voted for acquittal, Augustus made a law which required that convictions in trials in absentia had to be by unanimous vote.

The only other information we have is form Suetonius who said that Maecenas had betrayed the secret of the discovery of Murena's conspiracy to his wife Terentia and that Tiberius presided over the trial.

The Murena in question is probably Varro Murena who was consul suffect in 23 BC. Marcus Primus, the governor of Macedonia, was accused of declaring a war without the consent of the Senate. Murena defended Primus at his trial, who claimed that Augustus had ordered the war. This was a serious matter because under the First Settlement of 27 BC Macedonia had been designated a province under the jurisdiction of the senate and Augustus' ordering the governor of this province to wage war would have been a breach of the prerogative of the senate. Due to the gravity of the case, Augustus appeared at the trial even though he had not been called as a witness and under oath the denied giving any such orders. Murena felt that Augustus was subverting the trial and asked why he attended the trial even though he was not required to do so. Augustus said that he went there because it was in the public interest.