The key question is how far the obligation of disclosure extends.

Plainly there will have been some things on Martin's phone that would NOT have been evidence in this trial. For example if some weeks before his death he had been texting friends to arrange to go to see a film or a band - that would be completely irrelevant to the trial, and so under UK rules not obliged to be disclosed.

Equally, as Bobert says, material that might or might not have shown Martin with a gun or with drugs weeks before the night in question cannot possibly be evidence of anything happening on the night in question. What they might be is evidence of bad character and I would have thought that would clearly not be admissible - and so not evidence of relevance to the case.

It's interesting that (AFAIK) Zimmerman is still not relying on "Stand Your Ground" laws - is he?