To be caught red-handed is to be apprehended in the middle of committing a wrongdoing — not just suspected after the fact, but discovered in the act itself. There is no ambiguity: the evidence is present and undeniable. The image is of a murderer or thief caught before they can clean the blood from their hands.
The earliest recorded form is 'red hand' in Scottish parliamentary records from the 15th century. Scottish law used the phrase 'taken with red hand' to describe a criminal caught in the act of violence, with blood still on their hands as evidence of murder or assault. This was a serious legal distinction: a person caught 'red-handed' had limited grounds for defence.
The phrase entered mainstream English literature through Sir Walter Scott, who used 'red-handed' in his 1819 novel Ivanhoe and again in other works. Scott's enormous popularity spread the phrase rapidly across the English-speaking world. By the mid-19th century it was in common use beyond Scotland and had lost its strictly legal sense, applying to any wrongdoing discovered in progress.
No, not in modern use. While the original Scots legal term referred to bloodshed, the phrase now applies to any wrongdoing caught in progress — theft, deception, cheating, or any act someone would prefer not to be seen doing.
The phrases are near-synonyms. 'Caught in the act' is slightly more neutral; 'caught red-handed' emphasises that undeniable physical evidence was present, leaving no room for denial.