Year 1995. Sirius Black puts his hands in crystal clear river, it's not clear anymore, from blood on his hands. Just like his soul. Twelfth muggle. He is nearly done with becoming person they presented him for last fourteen years.
Pettigrew - exchange with Voldemort for someone far more valuable than the rat man.
Twelve muggles - not that much of a challenge, he's a wizard after all.
Potter betrayal - just about to happen.
A young boy emerges from the forest into his embrace.
"Aunt Petunia, sh-s-she's..."
"Shush, Pup, it'll all be over soon." - he is not wrong.
Shame that night is too dark for our golden boy to notice crimson stains on the river surface. Or dark glint that replaced gentle one in his godfather's eyes.
Or cloaked figure with snake-like face approaching them. Actually, that is the last thing our hero ever saw, followed by those two words Avada Kedavra, right after his godfather pushed him towards said figure.
Two days later Sirius could be seen crying on his godson's funeral. Man cleared of all charges, his Azkaban cell now holding a werewolf without a trial, he was supposed to keep watch of young Harry that night, but turned him over to Voldemort.
Convenient, how does a friend turn out a foe. Only he didn't, but they don't believe truth from his mouth. Only others who know are, now late Potter, and a foe.
Oh, how history likes to repeat itself...