Those cops sound like bad cops. That said, you may find you are better received in other similar situations if you approach with some form of medical ID or an opening statement declaring your medical care intent. That will help to differentiate you from people who just like to get involved (they do exist), who may be associates of the person cuffed (and therefore possibly pose a risk), etc. I realise there is a question mark over the legitimacy of the entire affair, given the officers' subsequent conduct with you, but you’ll never get to the bottom of that question conclusively because you came in halfway through. So the most effective way to do what you mean to do (which is both noble and right) is to introduce yourself in a way that eliminates any speculative risk-assignment to you. That way any further mishaps stand a better chance of being proven the result of corruption. I hope your injuries are better, and that you take this comment as a well-intentioned suggestion, not a way of passively assigning blame to you.