Deuteronomy 22:24
Then ye shall bring them both out unto the gate of that city, and ye shall stone them with stones that they die; the damsel, because she cried not, being in the city; and the man, because he hath humbled his neighbour’s wife: so thou shalt put away evil from among you.
The law prescribed death by stoning for adultery, holding both the guilty man and the guilty woman accountable under the circumstances it states. For a betrothed woman the outcome turned on place and outcry, distinguishing whether the act took place in the city and whether she cried out. A woman who was in the city and did not cry out stood condemned by that test.
Under the law governing stoning, the witnesses were required to cast the first stones, making them responsible for carrying out the judgment. This is the Mosaic law that the accusers invoked as the basis for demanding that the woman taken in adultery be stoned.