I've considered this event. It seems the accusers were obeying the Mosaic Law when bringing the woman to justice. Why did Jesus not fulfil this commandment? Was it because His presence on Earth was issuing in a new legal era?
Or something else?
It's a passage often used to decry that the law was suspended. However, Jesus never said that. As God, He was sinned against by the two having violated the law. He decided to forgive her.
As to the men who brought her before him we aren't told that they had any authority to stone her. Due process should have taken place and a ruling by the appointed judge.
These men were not there to carry out justice, but rather were trying to condemn the Just One.
The Just One was the only One qualified to offer Himself in place of her and all others.
Those who wish to be justified BY the Law will be judged by the Law.
Those who wish to be forgiven by the Redeemer must decide to trust Him alone without adding their own "good" deeds, mistakenly believing that God will cut them slack because they kept some of the law.
I hope this helps.