Institutio Oratoria

For there is no part of a speech so closely connected with any other as the statement with the proof, though of course such a digression may be intended as the conclusion of the statement and the beginning of the proof There will therefore sometimes be room for digression; for example if the end of the statement has been concerned with some specially horrible theme, we may embroider the theme as though our indignation must find immediate vent.

This, however, should only be done if there is no question about the facts. Otherwise it is more important to verify your charge than to heighten it, since the horrible nature of a charge is in favour of the accused, until the charge is proved. For it is just the most flagrant crimes that are the most difficult to prove.