On Wednesday, a grand jury will begin hearing evidence in the investigation of Michael Brown's shooting. The proceeding will ultimately determine whether Officer Darren Wilson — who, according to one autopsy report, shot Brown six times, including two shots to the head — will face criminal charges.

A grand jury is unlike a regular jury. Here's how it works and what we might expect when this one convenes.

What does a grand jury do?

A regular jury must decide innocence or guilt, which must be proven beyond a reasonable doubt. A grand jury has a different and less definitive role. "The main difference is that it is a lower standard. In a jury, you have to find that the person did the crime beyond a reasonable doubt," lawyer Collin Schwartz told The Wire. "In a grand jury, the defendant has no right to confront witnesses and it is only by preponderance of evidence, which is a lower threshold than reasonable doubt. It means more likely than not; much much lower than beyond a reasonable doubt."

Attorney Randy Kessler elaborated, "They don't decide guilt or innocence, they decide the probable cause to move forward. The defense doesn't have the right to cross examine the other side. There are two sides to the story. But the grand jury only has to side if there's one side to the story."

Who is on a grand jury?

The members of a grand jury have been selected by a judge, rather than by attorneys. This is part of why the process has moves more quickly, as a traditional jury selection process takes a great deal of time because lawyers can ask many questions of jurors, and strike some from the pool for any reason. 

This means that all members of this grand jury have likely heard of the case and its details. However, that isn't necessarily a bad thing. Kessler explains," The jury process is impossible. But a little known secret is that you don't want jurors who haven't heard about it, you want jurors who are sympathetic. So you want someone who has heard about it. But you don't want anyone who has heard a negative conclusion. It's okay to have people that have heard about it, but not been prejudiced by it."  

How did this get planned so quickly? 

Because the judge selected the jury, it is a much faster process. However, faster doesn't always mean better in a case of this sort. The prosecution has not had much time to build a complete investigation. For example, only two out of three autopsy results have come back. 

Jens David Ohlin, a professor of law at Cornell Law School, told The Wire that "Ideally, you have the police conduct a very exhaustive and deliberate investigation. Then after the files have been completely assembled, it is presented to the prosecutors who bring it before a grand jury, who decides if someone should be indicted. That is the usual and recommended course of events. You get the complete picture of the investigation and events before you get the grand jury case." Kessler agreed that the process was moving shockingly quickly. "If I were the prosecutor, I would want to wait till I have all the information," he said. 

Why are we going to a grand jury at all? 

The prosecutor does not have to go to a grand jury at all. In some cases, they can charge a suspect directly rather than wait for the input of a grand jury. However, going to a grand jury offers a major advantage to the investigation process: the prosecutor can subpoena witnesses. 

Ohlin also noted another motive for grand juries: it takes the pressure off the prosecution. "The fact that the prosecutor is empaneling a grand jury doesn’t mean that he wants to charge the individual. It just may mean he wants the grand jury to decide if the person should be prosecuted. Say you don't want the person to be prosecuted, and you think it is a borderline case, and you want a political cover for a decision not to prosecute someone, it is a lot easier to say a grand jury looked at the case. Rather than say 'I decided on my own to say there is no criminal case here.' In a borderline case, a prosecutor might empanel a case when they think the jury won't issue an indictment. I think that could be the situation here." 

Who is going to be in the court room?

"In general, for a grand jury, the prosecutor is in the grand jury room with the jurors. They are taking the jurors through the presentation," explained Ohlin, "Neither the defendant nor the defense attorney are in the grand jury room at all. They don't have a right to be there." The prosecution could also bring in witnesses who were subpoenaed. The proceedings and details of the case are secret and sealed to the defense and the public. The defense attorney will likely be present, however, he will not be in the room while the investigation is presented. 

Is Darren Wilson going to be there? 

There is a possibility Darren Wilson will be in attendance at tomorrow's indictment. Wilson has the opportunity to testify and he cannot be cross examined. However, lawyers are not present during questioning (though the witness can ask to leave the room to confer with them) and anything he says can be presented at a trial.

"I would think he would testify in a case like this," speculated Ohlin, "The only downside of testifying is if you think the grand jury is going to indict anyway. Testifying before the grand jury opens up the possibility that the prosecution could express any discrepancies between the grand jury and the trial. I would think his lawyer is urging him to get before the grand jury to tell a compelling story and hope the grand jury will refuse to return an indictment."

Kessler also believes a "compelling story" could sway grand jurors. He points out, "You also get some sympathy by being there. It is hard to indict someone you like." 

While Wilson is not legally obligated to be in court or testify, Schwartz believes he will still attend as a presence without taking the stand. "If I'm this guy, I'm not going in. I don't know who is going to be on the jury. The defendant will be in court but he doesn't have to take the stand." 

What is Darren Wilson going to be charged with? 

If he is charged, he could be charged with either murder, manslaughter, or second degree murder. Murder implies intentional killing and Ohlin notes that in that case, the "self defense argument doesn't work." Manslaughter and second degree murder are lesser charges, "based on the theory the defendant was reckless." 

What happens next? 

If he is indicted, the case will move to a trial. Even if the trial goes in Wilson's favor, Ohlin tells us "there is always the possibility of a federal criminal prosecution." If Wilson is not indicted, the case "could still move forward... But it gives you more grounds for appeal," said Kessler.