A more thorough explanation:

An investigative grand jury is a group of people, usually 23, who are chosen to sit for at least a month and sometimes up to a year. They meet in private and decide whether to issue indictments, which means formally charging someone with a crime. If the grand jury decides there is enough evidence to hold a suspect for trial, they return a bill of indictment.

The investigative grand jury has a primary function of examining possible crimes and developing evidence that is not currently available to the prosecution. This means they can gather information and evidence that can help determine whether there are grounds for a charge and can be used to prove the charge at the defendant's later criminal trial.

For example, an investigative grand jury may be used to investigate a case where there is not enough evidence to charge someone with a crime. They can subpoena witnesses and documents to gather more information and evidence to determine whether there are grounds for a charge.

Another example is when a prosecutor wants to investigate a case but does not want to tip off the suspect. They can use an investigative grand jury to gather evidence secretly and then decide whether to issue an indictment.