catch (someone) red-handed, to

To apprehend in the act of committing a crime. The term, which alludes to the presence of blood on the hands of a murderer, originally referred only to that crime. Later it was extended to mean the same as “to catch in the act,” an English translation of the Latin in flagrante delicto, taken from the Roman code and long used in law. “I did but tie one fellow, who was taken red-handed,” wrote Sir Walter Scott in Ivanhoe (1819).