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A presentment is a charging document returned by a
grand jury on its own initiative, without the involvement of a
prosecutor. So, if a grand jury heard about a murder, decided to charge
someone with murder (somehow came up with the form indictment to do so),
and voted to return the charge that would be a presentment.
An indictment is a set of charges drafted by a
prosecutor and submitted by the prosecutor to the grand jury. The
prosecutor asks the grand jury to vote to return the indictment, i.e.,
to charge the person(s) named therein. If they return it, it's a charge.