[18.117] For Herod had killed this good man, who had commanded the Jews to exercise virtue, righteousness towards one another and piety towards God. For only thus, in John's opinion, would the baptism he administered be acceptable to God, namely, if they used it to obtain not pardon for some sins but rather the cleansing of their bodies, inasmuch as it was taken for granted that their souls had already been purified by justice.
[18.118] Now many people came in crowds to him, for they were greatly moved by his words. Herod, who feared that the great influence John had over the masses might put them into his power and enable him to raise a rebellion (for they seemed ready to do anything he should advise), thought it best to put him to death. In this way, he might prevent any mischief John might cause, and not bring himself into difficulties by sparing a man who might make him repent of it when it would be too late.
[18.119] Accordingly John was sent as a prisoner, out of Herod's suspicious temper, to Macherus, the castle I already mentioned, and was put to death. Now the Jews thought that the destruction of his army was sent as a punishment upon Herod, and a mark of God's displeasure with him.
I see a very strange thing in Josephus.
Josephus introduces John as John "who was called the Baptist", but he doesn't explain minimally why this John was called "Baptist". This remembers the strange absence of explanation by Josephus about the construct "called Christ": in both the cases no explanation is there about the origin of the label for the guy who is going to be mentioned.
A possible objection is that Josephus really would describe why John is called "Baptizer" in the following sentences. But this is simply not true:
Josephus isn't explaining at all why John is named "Baptist". At contrary, he is introducing the "John's opinion" about the baptism only on the assumption that the readers know already that John was called "Baptist" because he was baptizing people. But clearly the Roman readers couldn't realize in advance the implication:For only thus, in John's opinion, would the baptism he administered be acceptable to God, namely, if they used it to obtain not pardon for some sins but rather the cleansing of their bodies, inasmuch as it was taken for granted that their souls had already been purified by justice.
Being called "Baptist" -------> being one who was "administering the baptism" to people
...not more than the same Roman readers could know who James was from the mere fact that he was the brother of a Jesus "called Christ".
Unless the readers of that particular version of Josephus were CHRISTIAN readers.
Unless the entire passage about John (or at least only about the his reference to the baptism and his label as "Baptist") was a Christian interpolation.