What is a Grand Jury?

In the past few days of global, we have been looking at the grand jury documents in the Ferguson Police case. So, what is a grand jury, and how come they decided that Wilson should not be prosecuted?

What is a Grand Jury?
When prosecutors believe a serious crime has been committed, a grand jury may be used to determine if there is enough evidence to go forward with a trial. The federal government and 50% of the 50 states use a grand jury. Grand juries generally consist of about 23 people and only hear evidence the prosecutor chooses to present. There is no judge and attorney representing the accused. The proceedings are kept secret and if the grand jury feels that there is enough evidence, it votes for an indictment and the case moves forward.

Trial Jury vs. Grand Jury
Regular citizens are randomly chosen from the same pool that makes up trial juries. They have no legal training. They convene for months at a time and only meet occasionally. They usually decide on many cases at a time. They are not screened for biases or conflicts like jury's are in trials. A trial jury needs to find a defendant guilty beyond a reasonable doubt, but a grand jury just has to determine that there is probable cause to proceed to trial. They don't decide guilt or punishment. Trial Jury's need to make a unanimous decision. The grand jury typically only needs a majority for an indictment. As a result, almost anything prosecutors want they get from a grand jury.

Why is it so hard to indict police officers?
Police automatically have qualified immunity which means they are allowed to do things that regular civilians would get in trouble for. The prosecutors and police usually work together building a case. When they are suspect, police and prosecutors are too close to each other so no one in the grand jury system that is there to advocate for the victim.

It is funny that grand juries first came to protect citizens from overzealous but now they seem like a way to protect police officers from prosecution.