YOU SAID:

Kill my best friend while he is sleeping.

INTO JAPANESE

彼が眠っている間に私の親友を殺します。

BACK INTO ENGLISH

You killed my best friend while he is asleep.

INTO JAPANESE

彼が眠っている間、私の親友が殺されます。

BACK INTO ENGLISH

While he is asleep, my best friend is killed.

INTO JAPANESE

彼が眠っている間は、私の親友が殺されます。

BACK INTO ENGLISH

While he was asleep, my best friend is killed.

INTO JAPANESE

彼が眠っている間は、私の親友が殺されます。

BACK INTO ENGLISH

While he was asleep, my best friend is killed.