Complex sentence: The coroner then informs Scully that he believes that this is a ritualistic killing with boiling of the bones in an acid to remove the flesh, the theory Scully had originally believed to explain the remains of Angela and Wallace.
Split into simpler sentences: The coroner then informs Scully that he believes the death to be a ritualistic murder, in which the victim's flesh was removed with acid or by boiling. This is the theory Scully had originally advanced to explain the remains of Angela and Wallace.