YOU SAID:
Why didn't you kill her
INTO JAPANESE
なぜあなたは彼女を殺さなかった
BACK INTO ENGLISH
Why did you kill her
INTO JAPANESE
なぜ殺した?
BACK INTO ENGLISH
Why did you kill her?
INTO JAPANESE
なぜ殺した?
BACK INTO ENGLISH
Why did you kill her?
That didn't even make that much sense in English.