catch somebody red-handed

catch (one) red-handed

To see, and perhaps apprehend, someone as they are doing something (often something nefarious). The phrase might have originally referred to blood on a murderer's hands. The police caught the robbers red-handed as they ransacked another house. Timmy tried to get into the cookie jar again, but I caught him red-handed.

catch somebody red-ˈhanded

find somebody while they are doing something wrong, committing a crime, etc: The thief was caught red-handed as she was emptying the till.This originally referred to catching a person with blood still on their hands after killing somebody.