I remember learning an interesting thing about this incident. Under the law the woman alone could not have been accused as it was required that both parties involved in the act of adultery were brought for judgement. Then both would be judged and punished according to the law.
If by the time of Christ, the adherrence to the law had been so corrupted that in such cases only the woman should be brought forward for judgement, it's another instance of the Pharisees getting a shock that Christ wouldn't go along with their twisted and prejudiced concept of the law. Christ was constantly at odds with the religious leaders about their corruption of the law; their additions to it that made it a burden, especially for those lacking social influence and the poor. This case is as blatantly unjust as the other times when Christ clashes with the religious leaders and almost has a hint of conspiracy about it.
If Christ had agreed that the woman should be punished without the male also being punished, He would have been guilty of breaking the true Law and then the religious leaders would at last have had something solid to accuse Him of. On the other hand, as He refused to comply with the Pharisaic and corrupted interpretation of that law, He again publically put them in their place and made even more bitter enemies of them.
As the woman was actually caught in the act of adultery, where was the male she committed the act with? Why wasn't he brought for judgement? Would the religious leaders have gone so far as to contrive this situation? Did they hate Christ that much and long to be rid of Him? Obviously, we can't know, but I wonder if Jesus, knowing this was a set-up, wrote the very requirements of the law? Seeing that their plan to ensnare Him had failed, they simply melted away.