The "subjective" reference of mens rea is to the mind of a person bent on legally proscribed harm doing. We cannot see these mental functions, nor can the most sensitive instruments record their operation. It seems likely that the first method of describing and explaining them was to point to and thus (illicitly!) call the attention of others to events and experiences, which obviously excluded the relevant conscious mental states.
Accidents e.g. are patently antithetical to intention, and overwhelming physical forces, tossing ships and houses hither and yon, also exclude any resulting bodily movements from the category of (voluntary) conduct. From the recognition that any man's body, moved by natural forces, was a mere object, it was not a great step to the exclusion of the mental states of feebleminded and psychotic persons from the sphere of mens rea. "Where there is a total defect of the understanding, there is no free act of the will in the choice of things or actions." (Hale, 1994)
The relevant meaning is communicated in the expressions that there was no intention, choice or "movement of the will." There was only behavior, the physical motion of material bodies, like that of sticks and waves. It is not difficult to imagine why negligent harm-doing was not, in early times, similarly excluded from the range of mens rea : For there was no outside operative force there, nor any serious mental disease; instead, the harm-doer was probably doing something intentionally.
According to the above-mentioned explanation, A should not be held responsible for the murder of C because he did not intend to kill her but his girlfriend, namely B. However, he should be held accountable for intending to kill his girlfriend, B. He should be however be held responsible for and prosecuted for intended assault on........
