I understand you to say that it never entered your head that the witnesses at the inquest could possibly have mistaken your voice for that of Mr. Inglethorp. 
I doubt that people would ever mistake your voice for that of Mr. Inglethorp. 
mnli hypothesis: I doubt that people would ever mistake your voice for that of Mr. Inglethorp.  premise: I understand you to say that it never entered your head that the witnesses at the inquest could possibly have mistaken your voice for that of Mr. Inglethorp. 