That can be difficult to do depending on the context. Mexico comes to mind. Criminals can use both fear and loyalty to make it harder to prove crimes and if politicians are involved, they can easily threaten other politicians or even the legal system itself. This isn’t to say that the approach won’t work, long-term de-escalating violence, increasing controls in arms trade, and asserting the rule of law above any individual are all viable. It’s getting the existing gangs and political systems to change their ways that is harder. It’s also worth pointing out that a justice system based on evidence can still serve unjust sentences, make mistakes. And politicians write the laws the system enforces. And many places don’t have free speech and human rights upheld to such an extent that laws can’t easily be written to curb it. So it’s a complicated problem... I’d even start by saying Panama Papers highlights a problem that you can have anonymous “persons” making transactions that are untraceable, etc. And countries and businesses can profit off this, and there isn’t agreement as to when privacy is worth more or less than free speech or when profit is valued more or less than security.