I’m So Crushed…..!!! Someone Plz Help Me?

So about 2weeks ago i was on my laptop and decided to download RealPlayer.
It then asked me if i would like my media to import into realplayer. i clicked yes .
i then went to the videos and found out that someone had downloaded alot of Porn.
I didnt really know who to blame since i let alot of people use my computer. i know it couldnt of been a virus because i have norton. i asked everybody and of course everybody denied it. i began deleting the videos and then i noticed the tittle of one of the videos it was titled “8YO ..etc”
CHILD PORNOGRAPHY!!! i was so crushed when i saw that because our family has gone through alot of molestation and its just messed up how after everything, somebody would still look this piece of crap?? i wanted to find out who. Luckily i love taking pictures and i noticed the day it was downloaded, i went to my pics and figured out what day that was. my brother had the computer all day that day. i cant really blame my brother because my brother brings alot of friends over. >.< my mind is just everywhere and i dont know what to think and im very crushed because i myself was molested and seeing sick **** like this gets me so angry. im really worried because i have a niece thats 4 and a nephew thats 2. i dont even know who to trust anymore i love those kids as if they were my own . ugh. someone please help me. oh and its not like i could ask my bro if he did it bc obviously he's gonna deny it and its just gonna spark drama.