The 5th Amendment of the US Constitution guarantees that all felony cases must be presented to a grand jury before it can proceed to trial.
A grand jury consists of 23 citizens. Their job is not to determine whether a person is guilty or not guilty, but whether there’s reasonable cause to believe that a crime has been committed, and whether that case should then go forward to trial.
In order for the case to go forward, 12 or more jurors must vote affirmatively. That's called a “True Bill” and results in an indictment. If less than 12 jurors vote affirmatively, then the case is dismissed. That's referred to as a “No Bill”.
A defendant, the person who is the subject of the grand jury proceeding, has an absolute right to testify before the grand jury. While in the grand jury, the defendant has a right to make a statement on their own behalf. During that process, the defendant will also be questioned by both the prosecutor and the grand jurors.
I deciding whether or not to testify, a defendant has to be extremely cautious, since the defendant is testifying under oath and is required to waive their immunity. Anything that’s said can be used against them later on if the case proceeds to trial. The advantage in deciding to testify is that sometimes the testimony of a defendant can convince a grand jury not to vote for an indictment, the case is then dismissed and the case is over.
Whether or not a defendant should testify before the grand jury is something that the defendant and his or her attorney need to discuss and evaluate very carefully. Although the ultimate decision lies with the client, an experienced attorney will weight the advantages and disadvantages of whether or not their client should testify. Some of those considerations include the factual strength or weakness of the case, whether the client is able to articulate a credible explanation about what happened, and whether the client can articulate a viable defense.
All those considerations need to be discussed and evaluated with an attorney who has experience with prior grand jury presentations, and who can properly advise the client to make the correct decision.