catch someone 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.
See also: catch
catch someone red-handed
COMMON If you catch someone red-handed, you see or find them while they are doing something illegal or wrong. The burglar was on the roof and was caught red-handed by the police. They all pleaded guilty to conspiring to import drugs after being caught red-handed by customs officers. Note: The reference here is to a guilty person whose hands are covered in blood.