Not to derail, but the #1 reason cops reach for their weapons is because they fear a suspect has a weapon. Its a split-second, life-or-death choice. No amount of martial arts training will change that.
I once saw a video of some experienced fighters practising some technique on an instructor who had a training knife they don't know about.
With all the excitement and adrenaline, not only did every single student get 'stabbed' - many of them didn't notice until the exercise was over and the instructor pointed out the 'stab wounds'.
I'm not sure there's any amount of BJJ that would make me confident to grapple a guy who could have a concealed knife.