Year 11 have left the building...but not without a fight!

Literally, I have never seen such physical violence in real-life, certainly not in a school. I was stunned. There were many, many individual incidents but I want to tell you about Brian*.
 
Brian is approximately 6 ft tall. Lunchtime of Thursday - Year 11’s last day (although they didn’t know it at this point) he picked up a chair and lunged towards a group of pupils, I had to run (those of you that know me will understand the enormity of that situation), stand in front of him and hold the chair before he would back down; he later took his belt off, tied it off wit the buckle exposed and used it as a very effectively weapon, causing cuts and welts amongst staff and pupils. 
 
Police
I am just over 5ft 3inches tall. There were other members of staff on site but they were dealing with similar situations throughout the site. Three different members of staff felt the need to call the police because of their incidents. Brian is going to be charged with affray; one other boy was handcuffed as he wouldn’t do what we or the police told him but he was later released without charge.
 
 
Examinations
Naturally Brian has been excluded. However, as he is in Year 11 and that was his last day this is actually causing me (as Head of Centre) more problems than it solves. Firstly as a result of the fight he missed his Spanish exam. I then had to find another examining centre (overnight) for him to sit his PE exam. 
 
I’ve found a Pupil Referral Unit (PRU) where he can sit his other exams but they’re charging us £100 a day for the privilege. His father is already talking about his human rights, our Headteacher thinks that we have to allow him to sit his exams somewhere (apparently this is the legal position or at least it is when we’ve not time to put alternatives in place). I can understand this because if he doesn’t then he’s a 16 year old, black boy who was permanently excluded from school and has no GCSEs to his name.
 
The school’s future
As I am leading on Key Stage 4 intervention and can already feeling the threat of another Ofsted and Local Authority inspection if our exam results don’t dramatically improve I really want Brian taking his exams and being in the right frame of mind when he does. However as I look forward to the new challenge of raising standards as a Deputy Head I don’t want the current Year 10 thinking that no matter what they do we need them more than they need us and they can do whatever they want and we won’t exclude them because we need their grades.
 
This gets me thinking about how school is judged. The story now will be that the police were called in to the school. I wonder how parents will feel about that. I also wonder how many of them will be thinking about what might have happened if we hadn’t called the police in? Later on, in August, the story will be our results. Our 5 GCSEs A* - C percentage; nobody outside of the institution will stop to consider that 2 boys were effectively held by the police during the exam period or that one boy had to sit his exams in unusual circumstances and unknown surroundings as a result.
 
I’ve re-written this sentence 5 or 6 times. I don’t’ quite know how to finish this piece, how to move on, how to remind myself that this one negative incident doesn’t mean that the whole school is about to tumble. 
 
I’d welcome your thoughts on the above and any advice on how to turn things around and move forward in the right direction.
 
* I have changed his name, even though you don’t know the school because this is an ongoing police matter.