SUETONIUS, Life of Tiberius
[XXII] Excessum Augusti non prius palam fecit, quam Agrippa iuuene interempto. Hunc tribunus militum custos appositus occidit lectis codicillis, quibus ut id faceret iubebatur; quos codicillos dubium fuit, Augustusne moriens reliquisset, quo materiam tumultus post se subduceret; an nomine Augusti Liuia et ea conscio Tiberio an ignaro, dictasset. Tiberius renuntianti tribuno, factum esse quod imperasset, neque imperasse se et redditurum eum senatui rationem respondit, inuidiam scilicet in praesentia uitans. Nam mox silentio rem obliterauit.
22. He did not make the death of Augustus public, before young Agrippa had been taken out. He was slain by a tribune who commanded his guard, upon reading a written order for that purpose: respecting which order, it was then a doubt,whether Augustus left it in his last moments, to prevent any occasion of public disturbance after his decease, or Livia issued it, in the name of Augustus; and whether with the knowledge of Tiberius or not. When the tribune came to inform him that he had executed his command, he replied, " I commanded you no such thing, and you must answer for it to the senate." avoiding, as it seems, the odium of the act for that time. Andthe affair was soon buried in silence.