catch (someone) red-handed, to

to catch a person in the act of doing something wrong. (See also caught red-handed.) Tom was stealing the car when the police drove by and caught him red-handed. Mary tried to cash a forged check at the bank, and the teller caught her red-handed.

Also, catch in the act. Apprehend someone in the course of wrongdoing, as in The boys were trying to steal a car and the police caught them red-handed, or He tried to cheat on the exam, but his teacher walked in and caught him in the act. The first term referred to blood on a murderer's hands and originally signified only that crime. Later it was extended to any offense. The variant ( catch in the act) is a translation of the Latin in flagrante delicto, part of the Roman code and long used in English law.

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).