How do say "pegar alguém no flagra ou com a mão na botija" in English?

To Catch someone red-handed (in the act)  - Pegar alguém no flagra ou com a mão na botija

Meaning 

To catch a person in the act of doing something wrong.

(Pegar alguém com a boca na botija.)

Example

Yesterday I caught Juan red-handed. He was cheating on the test.

(Ontem eu peguei o Juan no flagra. Ele estava colando no teste.)