Flavius Josephus, Antiquities of the Jews
William Whiston, A.M., Ed.

[317] After these, the commander of the garrison of Alexandrium was caught and tortured; for he was accused to have promised to receive the young men into his fortress, and to supply them with that money of the king's which was laid up in that fortress, yet did not he acknowledge any thing of it himself; but his son came ill, and said it was so, and delivered up the writing, which, so far as could be guessed, was in Alexander's hand. Its contents were these: "When we have finished, by God's help, all that we have proposed to do, we will come to you; but do your endeavors, as you have promised, to receive us into your fortress." After this writing was produced, Herod had no doubt about the treacherous designs of his sons against him. But Alexander said that Diophantus the scribe had imitated his hand, and that the paper was maliciously drawn up by Antipater; for Diophantus appeared to be very cunning in such practices; and as he was afterward convicted of forging other papers, he was put to death for it.