I wonder what are the "certain implications that arise when you do exercise" the right to silence the James Grant refers to? And also, why would a decision be made not to proceed with Carl wiping the mobile of its data?
I'm not a lawyer and your first question is not as straight forward as you may think. This is the best I can come up with but it relates to the law in England. That said, I imagine it's probably very similar in SA.
If, having considered the defence case,
the jury concludes that the silence can only sensibly be attributed to the defendant having no answer or none that would stand up to cross-examination, they may draw an adverse inference.
Sometimes an accused refuses to make statement because he intends to
fabricate a defence late in the day or he doesn't have a genuine defence or any fact which may go toward establishing a genuine defence.
To avoid the drawing of an adverse inference, some defendants will state that they remained silent because they were advised to do so by their legal advisor. The defendant's statement that he was silent on legal advice is not hearsay provided that the purpose is limited to explaining why the defendant decided to remain silent.
A jury should then consider whether it was reasonable for a defendant to rely on such advice.
In England, the Court of Appeal set out a two stage test for juries to consider before drawing an adverse inference:
1. Did the defendant genuinely rely on the legal advice, i.e. did the defendant accept the advice and believe that he was entitled to follow it? and
2. Was it reasonable for the defendant to rely on the advice? By way of example, a defendant may be acting unreasonably if he relied on the legal advice to remain silent because he had no explanation to give and the advice suited his own purposes.
Reasonableness does not depend on whether the advice was legally correct.
However, it is open for a jury to consider whether the accused did not respond to the police questions because his account would not stand up to questioning or any other adverse inference that they deem appropriate.
As to your question re Carl wiping the phone data, it appears the prosecution and defence made a deal at some stage during the trial. The prosecution agreed they wouldn't charge Carl for wiping the data in exchange for the defence not calling ex-Detective Hilton Botha. Botha was the lead detective in the investigation into Reeva's death. During the bail hearing when he gave evidence, he was heavily criticised for giving contradictory evidence, made to look ill-prepared and gave incorrect information. He was removed from the case after it emerged he was facing seven counts of attempted murder and he subsequently resigned from the SAPS.