You shouldn't have to ask others what you should do. What would you want somebody to do if you were the person who had been glassed? Just tell the Police what you witnessed and it’s up to others to decide where the guilt lies, it’s not your fault somebody was glassed. It could be your fault that Carroll gets off with something he has done or is found guilty of something he hasn’t. Just tell it as you see it and forget about it.
Doing nothing is wrong.