YOU SAID:

I an american is going to shoot this school up

INTO JAPANESE

私はアメリカ人がこの学校を撃つつもりだと思います

BACK INTO ENGLISH

I think the Americans are going to shoot this school.

INTO JAPANESE

アメリカ人はこの学校を撃つつもりだと思う

BACK INTO ENGLISH

I think the Americans are going to shoot this school.