I was going through NamUs and came across this UP. The location is what gets me, and while the clothes don't match, knowing it's a previously known homeless encampment strikes me as "those may not be his clothes." The age and height match too. Plus, if he had gotten someone else that bottle of CR, how unlikely would it be that he could have been met with foul play? I used to live in this area, and there are some questionable folks, even in Georgetown. I don't know if David ever suffered from knee issues, but would be a great help in identifying.
The National Missing and Unidentified Persons System (NamUs)
The National Missing and Unidentified Persons System (NamUs)