(8)If a person cannot be compelled to attend as a witness, or if owning to the exigencies of service or any other grounds (including the expense and loss of time involved), the attendance of any witness cannot, in the opinion of the commanding officer or the officer taking the summary (to be certified in writing by the commanding officer or such officer), be readily procured, a written statement of his evidence purporting to be signed by him may be read to the accused and included in the summary of evidence.
