Mass. Gen. Laws ch. 263 § 4A
A defendant charged in the district court with an offense as to which he has the right to be proceeded against by indictment shall have the right, except when the offense charged is a capital crime, to waive that right, whereupon the court shall have as full jurisdiction of the complaint as if an indictment had been found. If a defendant is so charged and requests a probable cause hearing in district court, that request shall constitute a waiver of the right to be proceeded against by indictment and the prosecution may proceed upon the complaint. If a defendant waives the right to be proceeded against by indictment, a probable cause hearing shall be held in the district court unless the defendant waives the probable cause hearing or unless the prosecutor elects to proceed by indictment pursuant to the Massachusetts Rules of Criminal Procedure.
If the district attorney desires to charge a defendant who waives indictment hereunder with an additional non-capital crime which is not charged in the complaint upon which the prosecution is proceeding and as to which there is the right to be proceeded against by indictment, the district attorney may prepare an additional complaint charging such additional crime and serve that complaint upon the defendant so as to give the defendant an opportunity to waive indictment upon such additional charge.
Mass. Gen. Laws ch. 263, § 4A