In the adversarial model of American jurisprudence, the prosecutor's job is to make the most rigorous case he can to convict, just as it is the defense's job to defend with all the rigor at his disposal. The presumption is that, by creating such an atmosphere, the truth will eventually out.
I agree that it is not the best model in the world. It is only better than anything else so far practiced.
Yes, the prosecution is obligated to reveal all RELEVANT evidence. But if he deems the evidence irrelevant or of dubious credibility, he may opt to not reveal it at all. That is his prerogative, and a sharp defense attorney will pursue ALL the evidence, regardless of whether the prosecution considers it relevant or not.
What this prosecutor did was a breach of the Canon, but does not rise to the level of a crime. In my opinion ...
Yes, the prosecution is obligated to reveal all RELEVANT evidence.
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No, The prosecutor is obliged to reveal all evidence. The prosecutor cannot later say “well, I didn’t think that was relevant so didn’t give it to you”, no, he has to give all there is.