Nelson said last week that Judge Richard J. Walsh will supervise the jury selection process.
"After the grand jury is selected, I expect the judge will review with them in detail exactly what their duties will be," Nelson said. The jury, clerks of the court, district attorneys and court stenographers will then be sworn to secrecy.
Nelson said the jurors won't be questioned about their knowledge of specific cases because "we don't know what cases we'll be dealing with."
While Nelson said in June he could not discuss specific cases the grand jury may examine, he said they could include "a number of unsolved homicides, as well as assisting police in investigating local drug trafficking organizations." The grand jury would not be limited to those areas, he added.
The supervising judge will appoint a foreman and 15 members will constitute a quorum, according to Nelson's June application to the court for the grand jury.
After being sworn in, the jurors can go home until Oct. 22-23, when Nelson said they will be called in to hear the first testimony. The grand jury will meet every other month for 18 months, but could be extended another six months if a majority of the jury votes that it has not completed its business.
Unlike a regular jury, the grand jury will not determine anyone's guilt or innocence. Based on evidence it hears, the jury can return presentments, a recommendation that criminal charges be filed.
Prepared by the District Attorney's Office at the direction of the jury, a presentment then goes to the supervising judge, who decides to refuse or accept the presentment. If accepted, the commonwealth may then file a criminal complaint.
In June, Nelson explained that he cannot subpoena anyone to testify in a case in which no charges have been filed. The grand jury has the power to subpoena witnesses that Nelson said have been unwilling to voluntarily give information.
Witnesses testifying before the grand jury cannot have an attorney present with them in the jury room. They can, however, consult with an attorney outside the room before answering a question.
Those who refuse to answer questions can, under some circumstances, be jailed for refusing to cooperate, Nelson said in June.
The grand jury presentments may be kept secret until a person is in custody or has been released pending trial, according to the application to the court.