Albert Barnes on John 8:9

Beginning at the eldest. As being conscious of more sins, and, therefore, being desirous to leave the Lord Jesus. The word eldest here probably refers not to age, but to honour--from those who were in highest reputation to the lowest in rank. This consciousness of crime showed that the state of the public morals was exceedingly corrupt, and justified the declaration of Jesus that it was an adulterous and wicked generation, Mt 16:4.

Alone. Jesus only was left with the woman, &c.

In the midst. Her accusers had gone out, and left Jesus and the woman; but it is by no means probable that the people had left them; and, as this was in the temple on a public occasion, they were doubtless surrounded still by many. This is evident from the fact that Jesus immediately (Jn 8:12) addressed a discourse to the people present.