flagrante delicto; caught red-handed
Refers to being caught in the act of committing a crime. Often used in legal or news contexts, but also in everyday speech for being caught doing something wrong.
He was arrested red-handed for shoplifting.
In some cases, you can't make an arrest unless it's flagrante delicto.
The police arrested the man in the act of committing the crime.
The thief was caught red-handed.