[ansy]

That's true everywhere. Nowhere solves 100% of its criminal cases. You must watch too many police procedural TV shows if you think the cops just march out of the office and catch the bad guy by the end of every episode. Lots of times victims don't cooperate with police, it's unclear what really happened, police can't find the perpetrator, the prosecutor decides there isn't enough evidence to pursue a trial, there's corruption involved, the perpetrator has significant financial resources to fight the case, or ultimately the judge or jury thinks the evidence is insufficient. Or most tragically, someone does get convicted and it's the wrong person! The perpetrator is still out there and an innocent person is unjustly punished.