The mail your "friend" received when he registered. Maybe something like "Congrats, x ! You just registered to our site, www.y.com. My name is z...". Blah, blah.
Exactly what is the evidence against you ? Are you a bully or something ? I'm pretty sure people would know who is the bully ; you or him.
Are you that one unimportant kid everyone laughs at ? I keep getting fat by my "friend". I really don't have friends. I have people I share classes with. They laugh at me, disrespect me, then rely on me. I hate most of them, except for 1 or 2, which are actually good friends.
Do you still have the history recorded in your browser ? A mail sent for registration ? Maybe talking to your parents and telling them the truth ? Just go for it. Humiliate those bastards. :D
A few months ago...
something happened when a "friend" of mine came round.
Cut a long story short he created an account on someone else's site pretending to be the site's owner. He also professed this fake accounts love for a girl.(who the site owner loves in real life)
He then pinned it all on me.
To make things look worse, I had recently had a fall out with the site owner.
All the evidence proved it was me and I had a concrete motive too.
I lost all my friends because of this.
I then became, how shall I put this, emotionally unstable.
To make matters a hell of a lot worse, the girl I love shouted a load of crap at me and told me I had made her life a misery and said I should leave her alone.
Also my teachers started calling me useless.
I am now an emotional wreck and I just want my friends and my love back.