It is always the goal to get a conviction, not to find the perpetrator. Tat is how prosecutors and cops look at tongs. The ‘search for the truth’ is not relevant in criminal cases.
And I worked as an investigator for a city attorney’s office.
Years later the naive parents of the yoot would say, in response to the yoot's anger that they didn't lift a finger (or a voice) to defend him "we trusted the police to do their jobs." ... in other words, they fed him to the wolves.
That yoot grew older, and realized the world is not perfect ... does not carry resentment ... but shakes his head when he watches 'making a murderer' and knows there are many people watching saying 'they are just doing their jobs' ... although in this case it was so blatant I think even the yoot's parents could put up only a weak case in favor of the police.
It's the fundamental principle behind why government must be kept small. It only leads to bringing out the worst in man. Pride, sloth, greed, ambition and blindness are the first 5 traits that come to mind. It's a faceless blob that has no consciousness that it's dealing with human beings.