One thought that I have is that another letter or two are in order. Is there a governing body that presides higher than this board? I would copy them on it, and stress the egregiousness of the exT's behavior, and your concern that if the behavior is allowed to continue, there will almost certainly be other victims.

I'd request a more detailed response as to what actions were taken previous to closing the case, and maybe even suggest that at the very least some rehabilitative efforts need to be considered for this individual, in order to prevent potential further abuse from occurring. Simply letting you know that a file has been closed, in response to the issues you've raised, seems inappropriate to the gravity of the situation. Even if, at worst, all they manage to determine is that they can't subscribe to the possibility that this person has done anything wrong, the nature of your inquiry with them warrants being addressed in a significant manner in the first place.

Unfortunately, it's easier for institutions to ignore most complaints, and so many do on principle alone; in other words, their first line of defense will be rejecting your claim and seeing if that doesn't just make you go away and thusly ease up their workload, so that approaching them additional times ends up being prerequisite to getting any real action taken at all. Because in truth that process really will discourage a huge percentage of complainants from bothering further.

And if after all that there are not additional actions taken, you can at least take comfort in the fact that the organizations implicated have been made well aware of the problem, and are likely at least handling the situation in some way internally, keeping a much closer eye on this person, even if they are not making more public admissions to you or others. You're accomplishing something just by bringing it to people's attention, though I sincerely hope it will achieve a result more reasonably commensurate with this person's transgressions.