YOU SAID:

you have to understand that the one i killed was me

INTO JAPANESE

あなたは私が殺したのは私だったことを理解しなければならない

BACK INTO ENGLISH

You must understand that it was me that I killed

INTO JAPANESE

私が殺したのは私だということを理解しなければならない

BACK INTO ENGLISH

I must understand that it was mine that I killed.

INTO JAPANESE

私が殺したのは私のものだと理解しなければならない

BACK INTO ENGLISH

I must understand that it was mine that I killed.