John the Baptist was killed because he was critical of the contemporary Herodian ruler, Herod Antipas. All of the sources agree on that, both Josephus and the testimony of the gospels. Exactly ...

In the reign of emperor Tiberius, Gallilean prophet John the Baptist preaches against King Herod and Queen Herodias. The latter wants John dead, but Herod fears to harm him due to a prophecy.