The explosion had left a ringing in his ears, dust in the air and a general sense of being cheated out of a good hunt. All these things lingered for less than a moment before Sirius could catch his bearings, after which he noticed the large lumps of rubble where a street once was.
A stupefy couldn't do this, despite the madness that had been all-encompassing a moment before. Bodies of muggles littered the streets and as Sirius stepped to the closest one, a bloody smear on the charred road took his attention. A finger. One severed just above the knuckle. Singular. Clean.
An off-key laugh echoed throughout the area. No spell could leave corpses scorched but leave a severed finger. Peter had done this, for what ever reason and Sirius only knew one thing for certain— he did not kill Peter.
Peter was alive. And out there. And Sirius might be the only one left alive to know what he had done. That he had betrayed James and Lily. That he had killed them. Almost killed Harry. The laughter stopped. Harry. Peter had betrayed the Potter's once, and was still alive to do it again. Urgency ran up Sirius's spine.
He needed to protect Harry, make sure he was safe. And he had been willing to go to Azkaban to ensure that, still was. But Peter was alive, and there could be Auror's on the scene any minute. The explosion wasn't subtle, Peter had seemed to wanted this to be public. Whatever this was. And Sirius hadn't killed Peter. But it looked like he had.
But. Peter was alive. And for him to ensure Harry was safe Peter needed to be dead. So Sirius tightened his grip on his wand and disapparated from the ruined street, footprints across the ash the only remainder of his presence at the scene.
He knew, appearing in his apartment of which was decorated in a fine layer of dust, that the stunt Peter had pulled would look as if Sirius had killed him. Killed the dozen or so muggles around them at the time. Staying at the apartment simply wouldn't be viable, not when those closest to Sirius thought him a mass murderer. So he grabbed the essentials, regretted leaving his bike at Godric's Hollow, and left the door open on his way out.
He would need to find Peter first, and when he did Sirius would make him beg for the Kiss. But before that, he would lay a few rat traps.