Hard as I tried, I could not find any reference to baptism in the OT (Old Testament to Christians, Hebrew Scriptures to Jovah's Witless).
I know that previous to John the Baptist, many religions, mysteries and cults baptized their initiates mostly either in blood, or in water. Never the Jews at that time or now. For the remision of sins, they just sent a goat to the desert.
Jesus did not obviously start the baptism thing. He was a follower.
Many questions arise. Was John a follower of a follower? This would make Jesus a follower of a cult that did not adhere to the OT.
I know they call it "dedication", but anyone can see it was a baptism.
Mark 1:4 And so John came, baptizing in the desert region and preaching a baptism of repentance for the forgiveness of sins.
If they follow a pagan custom, how come they call just about everything a pagan custom? They initiate their lives as JWs with a pagan custom.