"5. To be confronted at the trial by and to cross-examine the witnesses against him. Where the testimony of a witness for the prosecution has previously been taken down by question and answers in the presence of the accused or his counsel, the defence having had an opportunity to cross-examine the witness, the deposition of the latter may be read, upon satisfactory proof to the court that he is dead or insane, or cannot with due diligence be found in the islands."