Still, this seems like a case in which a grand jury would have been especially appropriate. The grand jury dates to Henry II's reforms, and its guarantee was demanded of King John in Magna Carta. It is a panel whose special purpose is to ensure that a jury of peers agrees that charges are appropriate, which seems especially to be proper in cases where there is tremendous political pressure on the government to find a way to bring charges against someone.
Thus the Fifth Amendment says:
No person shall be held to answer for a capital, or otherwise infamous crime, unless on a presentment or indictment of a Grand Jury.......except in certain cases pertaining to actual military service. Florida is standing on the fact that this is not a capital case, but it surely meets the standard of a charge of an "infamous crime." The level of publicity, and attending political pressures, seem to make this exactly the kind of case in which a grand jury would be most appropriate.
I'm sure there is a legal tradition of interpreting "infamous crime" of which I am unaware; but I'd like to ask you for the benefit of your education and experience in these matters.