I will repeat a point I have made countless times before. A child molester or rapist is a danger to the welfare of the community. He is reported to the secular authorities as preventative act of protection. The fact that the secular court will try him based on rules and procedures that are different than Torah or that they will punish differently then the Torah - is not a reason for not using them for protection. This fact is repeated by many gedolim - some of which are listed below. Many additional sources are found in my books on abuse - especially volume II. Furthermore not only circumstantial evidence is permitted but conviction based on a standard of less then absolutely certainty is also permitted - sofek rodef is treated as a rodef. [additional sources are in the commentary section]
In addition this case involved a mandated reporter who is required by secular law to report the alleged abuse. BM 83 provides a basis for requiring a Jew to comply with mandated reporting law. These issues have been discussed many times in many posts on this blog - as well as my 3 books on child abuse.
========================================
Steipler Rav (Within the Domain of Gedolei Torah Volume 2 page 557-560): … When Rav Lorenz told the story to the Steipler Rav, the Steipler screamed, “A Jew who sins and repeats that sin, it is better that he be punished in this world and not – G‑d forbid – in the World to Come.” He explained, “The punishment in this world is minor compared to what happens in the World to Come. Furthermore if you succeed in stopping the jail sentence he will continue to repeatedly commit this crime. It is better that he receive his punishment and perhaps learn self‑restraint…In addition if I give you permission and you testify for his benefit it is obvious that every newspaper and all the public media will publicize the matter and it will also be a chilul HaShem when he sins again…”
Rav Moshe Halberstam (Yeschurun 15 page 646): Let’s return to the original question concerning a wicked molester whose evil inclination forces him to sin and be wicked and it is possible to turn him over to the government in order that he be incarcerated in prison for a number of years until he calms down and returns to G‑d wholeheartedly. According to the sources we discussed before it is clear that there is no sin or transgression in handing him over to the authorities. In fact the opposite is true – it is a mitzva because by doing so he is caused to stop from doing the disgusting deeds. In addition we know that the government will not execute him. Therefore the essence of his punishment is that he will be forced to dwell for a number of years in prison. This will be beneficial to him in that they will assign him a psychologist or psychiatrist who will supervise him and his activities with a watchful eye. Perhaps he will be able to find a resolution of his torment by means of this treatment. So in such a case it is obvious that it is a good thing to save him and to save his family from his incestual attacks on them.
Rav Yehuda Silman (Yeschurun 15 page 662): … The commentaries explain that the obvious reason for not needing witnesses but they could rely even on circumstantial evidence is because this was not a court procedure to punish wrongdoers. Rather it was either done to obey the law of the kingdom or it was to stop someone from sinning. The Rashba is cited in the Beis Yosef that witnesses are not needed in such a case…”. That is because we are concerned only with the knowledge of truth in order to stop the harm and to make protective measures against iniquity. Furthermore according to what I said that even a doubtful rodef is permitted to be killed it is obvious that it is permitted for us to take protective action even if we have unresolved doubts.