There is an old saying among American lawyers (and in Tom Wolfe novels) that claims in the U.S., a grand jury could be convinced to “indict a ham sandwich.” The saying uses common lunch meat to explain the American legal system makes it easy to convince a grand jurors of someone’s probable guilt -- but will it stand the test of time in Ferguson?

A Missouri grand jury came to a decision Monday on whether to indict police officer Darren Wilson for the fatal shooting of 18-year-old Michael Brown. The process took three months.

First things first, the jury must decide if there was a crime

The grand jurors must reach agreement on whether a crime was committed at all. To do that, they must decide if there were reasonable grounds to consider Wilson guilty of any crime at all. To do this, the jurors gathered and evaluated the evidence and testimony presented to it. This is called “probable cause,” and is part of the Fourth Amendment of the U.S. Constitution. It differs from a criminal court trial where guilt must be proved “beyond a reasonable doubt.”

“The standard is lower than a jury trial in criminal court, where jurors must determine if there is proof beyond a reasonable doubt that a crime was committed,” according the Washington Post.

What kind of evidence?

Everything. Jurors must go through every piece of evidence no matter how small. All testimony, whether it be a witness or a social media posting, must be evaluated for credibility and taken into account before reaching a decision.

“The duty of the grand jury is to separate fact from fiction,” said Robert McCulloch, the St. Louis County prosecutor at a press conference announcing the jury’s decision.

After the crime, must come the punishment

If “probable cause” is found, jurors are then asked to agree on a charge. In Wilson’s case, the jurors were not given a suggested charge and so had to consider a variety of charges including first- and second-degree murder, voluntary and involuntary manslaughter, and the lesser charge of unlawful discharge of a firearm, according to CNN.

How does an indictment pass?

There are 12 members on a Missouri grand jury and nine must agree on a decision for it to be official, according to the Washington Post.  A St. Louis County Circuit Court judge selected each juror in May, according to KWMU, St. Louis. As this is a sitting panel, members were not selected specifically for Wilson’s case.

This process "enables the presiding judge to ensure that the grand jury is representative of the community," Peter Joy, a professor at Washington University Law School, recently told KWMU.