I think the term is being used out of context. This 'patsy' is actually just not the nonce you are looking for (because he doesn't exist). Not a patsy in the sense of the word as we know it, someone just to pin the blame on, but Amaral had the other part right; convenient. In the wide vicinity of the right place at the right time. Nonce, yes, thief, yes, actually did it, no, that's pretty obvious now.
Circumstantial evidence is dependent upon cogency on the unlikelihood of coincidence. Clearly HCW's evidence does not meet their own legal thresholds to even force an arrest - and it never will.
So I suppose a convenient patsy isn't a bad description after all, Snr Dr.
So how would Amaral come to the conclusion that CB didn't do it? I'm confused as Amaral said the Police knocked on his door but he was out. Did they search for him? Amaral says they ruled him out, how? Did they check his phone? If they did find him, then they would have seen he didn't have dreadlocks. If they found his van they would see it didn't have cartoon characters. Can you explain all that?