In my past I have lied, cheated, explained away and made excuses. Recently I betrayed my best friend as well. I'm not the sum of all that I've done wrong nor the sum of all I've done right. Good people do bad things as bad people do good things. The world isn't so black and white. I'm glad that not everyone I've met has assumed those same actions would be repeated again.
Solus, imo, you did NOT betray your best friend. You did what was right, and stood up and told the truth. In a way, you were Remy's salvation, because if he hadn't been stopped, if he'd gotten away with it (like he was so sure he would), who knows how far he would have descended -- who would have been his next victim? Remy's only hope is to be forced to suffer consequences for his actions (and hopefully...at some point...taking responsiblity) -- because otherwise he would think (as he apparently did) that he was above the law and could get by with murder.
It's like having children -- you're not betraying your children when you discipline them for bad behavior -- rather, you are helping them develop into good citizens. So, please, don't beat yourself up for being part of the process of bring Remy to the discipline he needed to face.
And as far as goodness and badness -- yes, a "good" person can do bad things, can make mistakes, but a good persons admits their mistake, takes responsibility for it, and then strives not to make the same mistake again.
And, I also wanted to add that in the interview, you were the voice of logic and reason and honor. I really liked what you had to say.