YOU SAID:

It's not illegal if the cat was already doing it when I walked in.

INTO JAPANESE

私が入ったときに猫がすでにそれをしていたとしても、それは違法ではありません。

BACK INTO ENGLISH

It's not illegal if the cat was already doing it when I entered.

INTO JAPANESE

私が入ったときに猫がすでにやっていたのであれば、違法ではありません。

BACK INTO ENGLISH

It's not illegal if the cat was already doing it when I entered.