Jewish Historian Josephus Independently Documents John The Baptist's Ministry

"But to some of the Jews the destruction of Herod's army seemed to be divine vengeance, and certainly a just vengeance, for his treatment of John, surnamed the Baptist.   For Herod had put him to death, though he was a good man and had exhorted the Jews to lead righteous lives, to practice justice towards their fellows and piety towards God, and so doing to join in baptism ... When others too joined the crowds about him, because they were aroused to the highest degree by his sermons, Herod became alarmed.  Eloquence that had so great an effect on mankind might lead to some form of sedition, for it looked as if they would be guided by John in everything that they did.  Herod decided therefore that it would be much better to strike first and be rid of him before his work led to an uprising, than to wait for an upheaval, get involved in a difficult situation and see his mistake.  Though John, because of Herod's suspicions, was brought in chains to Machaerus, the stronghold that we have previously mentioned, and there put to death, yet the verdict of the Jews was that the destruction visited upon Herod's army was a vindication of John, since God saw fit to inflict such a blow on Herod."

Source: Antiquities of the Jews by Flavius Josephus, 18.116–119.