I totally agree with saving his life, and looking at the pictures one can only assume he does the next floor up in the same manner?
But give the guy a chance first by telling him what you are going to do if he does not change his methods?
One would also assume that the company that your friend works for would also be liable for employing him and allowing he to clean there windows in this manner.
your friend would not be to popular with there employer if they went the route of just reporting them, if no one listens to him/her then send in the pictures, I would have thought HSE will act quickly in this case, So the window cleaner and your freinds company would have to act even quiker.