I did originally think he succumbed to a brain injury near the river, and was rolled in after collecting any useful belongings, since the shirt possibly wound up on someone else.
The interaction with the officer made it seem that his injury was a lot less damaging than I had initially thought though.
We saw him run more than once and knew he was hitting concrete, bushes etc. so the idea of him accidentally careening into water seems very plausible at this point.
I just want to know more about the shirt! I very much believed the woman who saw it while volunteering, and said she had 3 or 4 other volunteers confirm they indeed saw a very similar clean shirt on a homeless man just after. <modsnip: not an approved source>
Moo