The US Supreme Court has said that you must invoke your right to remain silent. It doesn't seem constitutional, but it is currently the law. (Salinas v. Texas and People v. Tom)
That's not entirely true. They ruled that silence in a non-custodial interview could be admissable at trial. Silence in custodial interviews is still not admissable and they didn't actually decide the question of whether or not silence can be taken as substantive evidence of guilt.
What is "silence in a non-custodial interview" and how is that different from no interview at all?
It means remaining silent when you are not under arrest or being detained.
Sadly the court considers detainment to be non-custodial and rarely do they venture to better define when a detainment turns into an arrest.
GP's point is that the transcript did help.
> The shock and surprise of the accused was palpable from the transcript and believeable.
They are refuting the prior point -- that if the accused had been silent (when asked questions in the transcript) it would have looked like they were guilty. So this point is -- in U.S. it wouldn't, because they wouldn't even be discussing the transcript. (IANAL and have no idea of the accuracy, just clarifying the argument).