So, your goal is to simply forget?
Believe me, I have tried forgetting many things. But it didn't work, it kept rising to the fucking surface.
So I am pretty experienced in this. Or at least I find myself to be.
The only REAL way to forget about it is to deal with it, and efficiently.
If your friends have given you this conscience, Step 1 is to talk to them about how you feel like shit.
If you don't feel at ease after that, and still nervous, you have to do something about the matter of hand. This might be calling the police if this would be illegal and twisted.
Step 2 is to likely cut the bonds with those bastards for what they've done. Show you won't stand for it.
By now they might be angry at you for calling the feds anyhow.
And it's one step closer to moving forward with your life.
Also, for your own safety... Ask for a witness protection program.
Step 3. You could contact the victims or loved ones of these "inhuman" acts.
If you talk to them and still being humble, promising you have had these guilt trips for something you might not have done, if they forgive you, it can take a hefty load off of you.
Paying back and making amends really soothes the soul.
After that, you might just be feeling better and you're ready to "forget".
None of it is easy, and it might not turn out exactly like this, but you have to deal with it. It's NOT going to leave you alone. Not until you've found your answer.