from
Bouvier's Law Dictionary, Revised 6th Ed (1856)
FLAGRANS CRIMEN. This, among the Romans, signified. that a crime was then or
had just been committed for example, when a crime has just been committed
and the corpus delictum is publicly exposed; or if a mob take place; or if a
house be feloniously burned, these are severally flagrans crimen.
2. The term used in France is flagrant delit. The code of criminal
instruction gives the following concise definition of it, art. "Le delit qui
se commet actuellement ou qui vient de se coramettre, est un flagrant
delit."