Josephus Antiquities of the Jews Book 18.5
2 Now some of the Jews thought that the destruction of Herod’s army came from God: and that very justly, as a punishment of what he did against John, that was called the baptist. For Herod slew him would be acceptable to him, if they made use of it, not in order to the putting away, of some sins but for the purification of the body: supposing still that the soul was thoroughly purified beforehand by righteousness. Now when others came in crouds about him; for they were very greatly moved by hearing his words; Herod, who feared lest the great influence John had over the people might put it into his power and inclination to raise rebellion: (for they seemed ready to do any thing he should advise:) thought it best, by putting him to death, to prevent any mischief he 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. Accordingly he was sent a prisoner, out of Herod’s suspicious temper, to Macherus; the castle I before mentioned; and was there put to death. Now the Jews had an opinion, that the destruction of this army was sent as a punishment upon Herod; and a mark of God’s displeasure to him.
Mark 1:4
2 As it is written in the prophet Isaiah, “Look, I am sending my messenger ahead of you, who will prepare your way, 3 the voice of one shouting in the wilderness, ‘Prepare the way for the Lord, make his paths straight.’” 4 In the wilderness John the baptizer began preaching a baptism of repentance for the forgiveness of sins. 5 People from the whole Judean countryside and all of Jerusalem were going out to him, and he was baptizing them in the Jordan River as they confessed their sins. 6 John wore a garment made of camel’s hair with a leather belt around his waist, and he ate locusts and wild honey.
Notes and References
"... In Matthew’s narrative of the Baptist, there is no mention of forgiving sins. Although Luke conveys Mark’s wording about the baptism of repentance preached by John, he links the forgiveness of sins with the person of Jesus and with His ministry continued by His disciples. The issue of the relationship between the ritual performed by John and the liberation from sins is also addressed by Josephus Flavius. Regardless of the evangelical tradition, Josephus Flavius (Antiquities of the Jews 18, 116–117) mentions John’s activities and his baptism, citing the opinion of some Jews on the cause of the defeat suffered by Herod Antipas at the battle with Aretas IV at Gamala in Perea. According to them, this defeat was God’s punishment for killing 'John called the Baptist' ..."
Malina, Artur "Baptism of Repentance for the Remission of Sins" Mark 1:4 in its Context (pp. 689-707) The Biblical Annals, 11/4, 2021