Let me put it another way.
The defence will want to open the entire history of the case and all the suspects, throw their arms in the air and say how can these suspects all be positively eliminated one by one?
HCW will want to eliminate all those suspects via pieces of evidence against CB that are so strong, the other suspects must logically be ruled out, without having to examine evidence into each theory.
To use reductio ad absurdum - if HCW were now to find the victim buried at the box factory, then logically all other theories don't matter on the murder charge. You don't have to even consider them. No process of elimination is needed.
But as you step through evidential scenarios against CB that are less strong, all the theories can start to come back.
For instance, say the only evidence against CB is his confession(s), the phone call, and the Jag, Tannerman would be useful to the defence IMO.