USA has 95% convictions based on plea deals, so the investigation is only complete enough to convince the accused that he is isolated enough in his jail that he won’t be able to build a defense, but the accusation is never formally proved, it’s just the accused who agrees to admit crimes. Examples vary, for example pharmacists who are legally authorized to sell legal cannabis have been convicted because they couldn’t bring proof.
In France we have jihadists who get freed, rapists who get away with it because they are recently immigrated and « don’t have the western codes » (true quote from the judge), people who get French nationality after having assaulted a policeman; We also have people in jail for way lighter offenses, but who are public cases with lots of media pressure.
Although I’m all for a severe justice system, and process-based justice, I’m not convinced half of the convicts are there with a proven proof from the accusation ; rather, they couldn’t defend themselves.