Before saying anything else I'm afraid the term 'without prejudice' can only be used when a predefined set of conditions are met. From the sound of it they will not be met here and the institution and the persons named may indeed regard your letter or email as a legal matter on which they may take action.
Should you wish to do this please seek competent legal advice first. As you quite rightly say any court action may be as traumatizing as the original event - and maybe set your conditon back years - and is by no means likely to succeed without corroborating evidence and reliable witnesses as well as considerable expense.
Remember the first thing you are doing is suggesting poor performance by the principal, and secondly negligence or even abusive activity by those you name.
Most states have a special section of the police to which one can report abuse. I would suggest if you really want to take the matter further then start there though I suspect they may tell you the same thing. Ringing 1800RESPECT may also be useful.
Sleepy has a very good question in waht do you hope to gain? For many there comes a sense of validation and lessening of guilt if a perpetrator is stopped or brought to task, however I believe the majority find realistically the price far too high.
A list of bullying tactics is a useful thing, and it may help you in the writing, I guess I'd talk to my psych about that. To do anything with that list would take careful though and advice
I'm sorry to seem negative but would not want to to become enmeshing in something with your eyes closed.
I'd be glad if you wrote more