The tears running down Sirius’ cheeks and the way he's yelling “I didn't do it!” over and over in a way that makes the anguish clear in his voice makes it almost believable.
Remus wants to believe it, he wants to more than anything in the world. But he doesn't. He can't. Not when all the evidence points to Sirius.
There isn't a single thing that says he's innocent, and it makes Remus feel like he's being ripped apart.
It gets even worse when Sirius sees him and something akin to hope lights up in his eyes, like he thinks Remus will swoop in and save him.
And he might have, if this was a few years ago and Sirius was only getting busted for some stupid prank. But it's not.
When did it go from stupid, harmless pranks to murder?
“Moony.” His tone is pleading, desperate. “Moony, please. You know I wouldn't do this. You know I loved them more than anything. You know I did. I didn't do this.”
Remus shakes his head. It's all he can bring himself to do. He knows he can't speak, the words would just get stuck in his throat.
Sirius stares at him, eyes full of disbelief. “Please, you know I wouldn't do this! Moon– Remus,” he's falling apart, voice breaking, “Remus, please! You know me! You know I wouldn't do this!”
Remus feels sick, his stomach is churning, and he feels bile clawing its way up the back of his throat. He closes his eyes, wills himself to wake up, because this has to be some horrible nightmare. This can't be real. It can't be.
He knows he's crying when he opens his eyes, he feels the tears slip down his face.
Sirius is still looking at him with begging eyes. “Remus, you know me. I would never do this. I know you know that.”
Remus looks away when he says, “Do I, though? Apparently I don't know you as well as I thought I did.”
He keeps his gaze on the ground in front of him even when he hears a broken sob of “Remus.”