Sirius didn't know what to think when Dumbledore managed to find him at the Ministry, while he was in class no less and even managed to get everyone to leave the room with just a few words - Sirius always had found that ability of Dumbledore's to be pretty amazing.
When he started immediately into a conversation about Peter though, Sirius knew it couldn't end well. Not unless Dumbledore was here to tell him that Peter was being carted off, or they were bringing in a dementor - which given the man in front of him, he highly doubted either was the case.
"I've heard." He nodded, and as much as he'd wanted tout around the fact that he'd been saying Peter was a traitor from the beginning he'd kept it to himself, content with knowing Peter was doing the work for him.