catch red-handed

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.

to discover someone doing something illegal or wrong (often + doing sth) I caught him red-handed trying to break into my car.

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.