Under the Federal Rules of Evidence, Res Gestae is an exception to the rule against Hearsay evidence. Res gestae is based on the belief that because certain statements are made naturally, spontaneously and without deliberation during the course of an event, they leave little room for misunderstanding/misinterpretation upon hearing by someone else (i.e. by the witness who will later repeat the statement to the court) and thus the courts believe that such statements carry a high degree of credibility. Statements which can be admitted into evidence as Res gestae fall into three headings:
(In some jurisdictions the Res gestae exception has also been used to admit police sketches.)
The following scenario is an example of types one and two:
Imagine then a young woman standing on the side of a main road (the witness). She sees some commotion across the street. On the opposite side of the road to her she sees an old man shout 'The bank is being robbed!' as a young man runs out of a building and away down the street. The old man is never found (so can't appear in court and repeat what he said) but the woman repeats what she heard him say. Such a statement would be considered trustworthy for the purpose of admission as evidence because the statement was made concurrently with the event and there is little chance that the witness repeating the hearsay could have misunderstood its meaning or the speaker's intentions.
Under the Federal Rules of Evidence, Res Gestae may also be used to demonstrate that certain character evidence, otherwise excludable under the provisions of Rule 404, is permissible, as the events in question are part of the "ongoing narrative", or sequence of events which are necessary to define the action at hand.
For a technical explanation of Res gestae under English law See: WikiCrimeLine Res gestae
Res gestae is also used to refer to those facts or things done which form the basis or gravamen for a legal action.