If you have evidence that the assault occurred, why not contact the authorities yourself?
Seriously. He has public trust in his position as a firefighter and as such may have increased access to potential victims. You would be doing a public service if you wrote a note to the ethics committee of your government, with a cc to the police department, providing dates, names and all details possible.
Doing so may very well save one or many from being raped.
Also, justice would be a legitimate motive for turning him in. He ruined this poor girl's life and her family's, and now he's collecting a nice salary and benefits package from you the taxpayers, with greater ability to reoffend.