Our standard is "beyond a reasonable doubt" and ideally in a working justice system, judges should be throwing out any evidence which is prejudicial. So your detective has a general motive to find as much evidence as possible, overwhelming evidence, ideally, such that after all legal challenges have been passed through there is still enough evidence left on the table to concretely prove a case.
Obviously there's a lot of places our justice system can and does break down, but it is generally designed on the concept everyone involved in prosecution and defense should work to create the best possible case for their understanding.
What normally happens in cases like this is that each side barter with what they have (DA: "we went through his phone and found photos of him with guns, drugs and money" vs. PD: "the search was illegal, if you pursue this I'll file for suppression") to get the longest sentence they can (DA) vs. the shortest sentence (PD) on a plea deal.
I think the statistic is maybe 1% of criminal cases go to trial?
Most other countries don't have the concept, or if they do, its use is generally fairly minimal, and heavily regulated - oftentimes, it might be "plead guilty to this one murder" in the case of a multiple homicide, to avoid having three separate costly trials.