YOU SAID:

I saw someone steal my bike

INTO JAPANESE

だれかが私の自転車を盗む見た

BACK INTO ENGLISH

Someone is stealing my bicycle I saw

INTO JAPANESE

私は見た私の自転車を盗み

BACK INTO ENGLISH

I saw my bike to steal

INTO JAPANESE

私は見た私の自転車を盗むために

BACK INTO ENGLISH

I saw my bike to steal