A magistrate, who after several hearings had failed to discover, among a gang accused of murder, what was essential to the completion of the case, namely, the actual hand which struck the fatal blow, notified the prisoners that he was about to invoke the assistance of the spirits, with a view to elicit the truth.
Accordingly, he caused the accused men, dressed in the black clothes of criminals, to be led into a large barn, and arranged around it, face to the wall. Having then told them that an accusing angel would shortly come among them, and mark the back of the guilty man, he went outside and had the door shut, and the place darkened.
After a short interval, when the door was thrown open, and the men were summoned to come forth, it was seen directly that one of the number had a white mark on his back. This man, in order to make all secure, had turned his back to the wall, not knowing, what the magistrate well knew, that the wall had been newly white-washed.
(THE CIVILIZATION OF CHINA, by Herbert A. Giles)