I would say the goal is probably securing a conviction for the crime the detective believes took place: Closing the case is not inherently enough, and while there are some, I doubt most investigators sleep well at night that they convicted someone they think is innocent.
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.
I've never met an DA investigator or a DA that gave a single hoot if someone was factually innocent (this is actually rare). Even this "going through the phone" thing might be ruled illegal, but that only matters if the case goes as far as filing a motion to suppress. And if you are represented by a public defender then I would say your chances are slim at having that happen.
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?
Yeah, the US (mis)uses the plea deal to an appalling extent. It's amazingly fucked.
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.
I think a big part of the problem is if a person goes to trial in the US, if they still get a charge, even if it is much lower than what they were originally charged with, they are on the hook for all the court costs on top of all the fines and fees and jail costs and 10 different line item charges they will get already. And most people balk at the exorbitant costs when it is presented.
Hah, in Florida, if you spend time in jail, even if charges are dropped or you are found not guilty, you will still be billed for your incarceration. And failure to pay this is a ... you guessed it ... criminal offense.
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.