I am wondering when Jews began the tradition of kosher butchery as such. The Torah is not very specific about how meat is to be slaughtered even for sacrifices:
Thou shalt slaughter of thy herd and of thy flock, which the Lord hath given thee, as I have commanded thee, and thou shalt eat within thy gates, after all the desire of thy soul” (Deuteronomy 12:21).
The Jewish Encyclopedia says
There can be but little doubt, however, that in slaughtering the sacrificial animals the priests followed some uniform mode akin to that which was later adopted by all Israel and which is known as "sheḥiṭah"... Speculating on the etymology of the words "shaḥaṭ" and "zabaḥ," the Rabbis endeavored thereby to establish on a Scriptural basis the law that an animal should be slaughtered by cutting the throat.
This can be done by anyone who owns cattle. I'm looking for written historical sources (as opposed to the Oral Law) about the development of kosher butchery as a profession.
The earliest reference I can find is Sifrei Devarim. Are there earlier ones than this, either historical or scriptural? Information regarding the early history of kosher butchers (those who slaughter the animal according to halacha), beyond the tradition of draining the animal's blood, would also be appreciated.