I don’t know what the law was regarding mandatory reporting in 1981 but I think if there was such the principal certainly would fall under the category of those obligated to do so. I wish the article indentified him.
It is very difficult to substantiate 20 year old accusations which is one reason for the statutes of limitations. It does not mean a party is not guilty it just means there is not enough evidence to determine the facts. However if the incident had been reported in 1981 the evidence would have been fresh and the likelyhood of establishing the facts much higher.
The article does not indicate that the archdiocese was informed in 1981. Both they and the police should have been told at that time.
Thus we now know the reason for Crimen Sollicitationis and the victim and his family being sworn to the "oath of papal secrecy" under threat of excommunciation.
The victim is told not to go to the police but to report the abuse to a priest. The priest may or may not decide to go to the bishop. The bishop then dithers, stalls, and eventually denies anything untoward took place, as in this story.
End of discussion. The victim is silenced and the priest is free to continue to rape children.
It's no surprise it may take years for some of these crimes to see the light of day.
The real question is, of course, why didn't the priests/bishops/diocese go directly to the police when this accusation was made in 1981?
Read the Grand Jury report. It gives us a clue.