“The engagement of a magistrate to an accomplice, that if he will give his evidence, he will experience favor, is merely in the nature of a recommendation to mercy, for no authority is given to a justice of the peace to pardon an offender, and to tell him that he shall be a witness against others. He is not therefore assured of his pardon, but gives his evidence in vinculis, in custody: and it depends on his behaviour, whether he shall or shall not be admitted to mercy.” 1 Joseph Chitty, A Practical Treatise on the Criminal Law 82–83 (2d ed. 1826).
in vinculis
in vinculis (in ving-ky[schwa]-lis). [Latin “in chains”] In actual custody.