PrimeWire

I need someone to translate this for me, b/c you’re talking to someone who doesn’t know anything at all about the criminal justice system. As I understand it, if a crime is committed, one calls the police. The police come, investigate, gather evidence, and decide if a crime has been committed, what crime was committed, and what to charge them with. The district attorney then files the charges and the police arrest the person. Sometimes a jury is called during the trial and sometimes it isn’t. I don’t know when the DA calls a jury and when they don’t.
I know the above statement isn’t accurate, but I don’t understand all of this. What is the difference between an indictment and charging someone with a crime? If the DA here has millions of pages of financial evidence against Tramp, why not just arrest him? Why is the DA calling any jury at all? This is when I need Ms. Maddows to spend half of her show explaining this stuff.