YOU SAID:

i didn't start the fire

INTO JAPANESE

私は火を起こさなかった

BACK INTO ENGLISH

I didn't set the fire.

INTO JAPANESE

私は火をつけなかった。

BACK INTO ENGLISH

I didn't set it on fire.

INTO JAPANESE

私はそれを火にかけなかった。

BACK INTO ENGLISH

I didn't set it on fire.