The answer to all three of your questions is a conditional no. You generally do not require releases from public officials when filming them in their role as a public official. A release is, however, an insurance policy, of sorts - protecting you against the individual suing you over their depiction in your film.
When using only a portion of what the Attorney General's representative said during the hearing, you must be very careful with your editing, to ensure that the statements made by the representative, even in edited form, remain a fair and accurate account of what was said. In addition, you should be careful to use the videotaped statements in a context that does not alter the meaning or intent of the representative's words.
I am assuming here that the videotaping was done by you (avoiding any copyright issues over the rights in the film), and was not "covert," and was not done during a closed proceeding, and that your filming was not done contrary to any "decorum orders" that imposed restrictions on the use of cameras or recording devices during the proceeding. Grand jury hearings are generally secret, family court proceedings can be confidential, and juvenile delinquency hearings are often closed-door proceedings, for example. In addition, some courts have rules about filming jurors, sidebar conferences, etc. If you followed all laws, and court rules and regulations, with regard to your filming, you are probably okay.
I recommend you have an attorney review, before publication, the videotape as it is to appear in your documentary (and a review of your whole documentary would be wise) to make sure you are nicely avoiding defamation, privacy, infringement, and other legal issues. Whenever you are filming real people, you run the very real risk of a lawsuit. Having insurance covering your production is a wise idea.
