"Of itself the making of a pre-prepared statement gives no automatic immunity against adverse inferences under s.34 ... It may be incomplete in comparison with the defendant's later account at trial or it may be inconsistent with that account. This court notes a growing practice, no doubt on advice, to submit a pre-prepared statement and decline to answer any questions. This, in our view, may prove to be a dangerous course for an innocent person who subsequently discovers at the trial that something significant has been omitted. No such problems would arise following an interview where the suspect gives appropriate answers to the questions."