Assuming that someone else did dispose of body would that make DW innocent or an accessory ?
I think if you believe someone else dumped the body, then you really have to acquit Westerfield. There would simply be too many unanswered questions to convict him.
Despite the intense scrutiny DW was under (surveillance, phone records, GPS tracker on his vehicle, etc.), the prosecution did not turn up any evidence of a possible accomplice. Of course, that doesn't absolutely prove he didn't conspire with someone else to commit the crime. But I think to convict you would need evidence of a conspiracy.
The burden of proof falls on the prosecution. The benefit of the doubt must go to the defendant.