YOU SAID:

know the other was in the room were it happened

INTO JAPANESE

他の人が部屋にいたことが分かった

BACK INTO ENGLISH

I found out that someone else was in the room

INTO JAPANESE

他の誰かが部屋にいることがわかりました

BACK INTO ENGLISH

I found someone else in the room

INTO JAPANESE

部屋で他の人を見つけました

BACK INTO ENGLISH

I found another person in the room

INTO JAPANESE

部屋で別の人を見つけました

BACK INTO ENGLISH

I found another person in the room