いるところを見つけた

caught someone in the act

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phrase Rare #45,469
caught someone in the act Used when someone discovers another person while they are doing something, often something they should not be doing.
JA: 母は私がこっそりお菓子を食べているところを見つけた。
EN: My mother caught me secretly eating snacks.

先生は学生が試験でカンニングをしているところを見つけた。

The teacher caught a student cheating on an exam.

彼らは彼が妹に悪ふざけしているところを見つけた。

They caught him playing a prank on his younger sister.