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. A: "I swear, it wasn't me!" B: "Save it! The security camera caught you red-handed!"

caught red-handed

Seen or apprehended in the act of doing something, especially something illegal or nefarious. He tried to deny that he had stolen the money, but he was caught red-handed by security cameras. The robbers were caught red-handed as they ransacked another house. A: "Timmy did try to get into the cookie jar again, he was just caught red-handed." B: "Aha, so that's why he's in time-out."