If that happened as the op says, it's absolutely worth trying to bring the rapist and those who should have punished him but covered instead, to justice.

It will cost several hours over couple of weeks to remember and assemble the facts and submit them (remotely). Again, it's important to not harm the victim again. That's why going through the authorities is critical, and choosing the right level - I would not report to the same town or administrative area, especially if the offender works there. If done right, chances for success are high (of course, don't bring in any Navalny or similar topics, approach it as a criminal case). Only if all possible applications to authorities fail, consider going public, but weight that in with double care about the victim.

When the op was young and in the environment where no-one acted, it's possible to understand he didn't act till now. But now, IMHO, reporting this is the only right thing to do.

BTW, in many jurisdictions, failure to report a serious crime, especially against children, constitutes a crime by itself.