Given his living circumstances,I don't find it to be telling at all.It's possible,that while living under a bridge,he didn't invite to many friends or relatives over for dinner that day.Them not being able to exclude him may just be something as simple as he had no one to back up his story that he was under a bridge in a different town.But just because he had no one to verfy his story,doesn't mean it didn't happen just as he said.
I agree with you. I frankly don't think LE believes DN to be BG. What I don't understand is why they just won't come out and clear him... they don't need him to have an alibi, they just need to check his DNA against DNA they have from the crime scene.