Three things.

1) Whoever killed my sister will pay, especially because she is a blabbermouth. So Sirius Black killed her, a prime target for cop investigation or lynching, as he is probably scum because the other kill was a mafia.

2) We have 2 killing factions. So we have three good possibilities. Two mafia (I really hope not) A serial Killer ( Not as bad as two mafia, but still bad) or a vigilante (Best case Scenario)

3) We messed up with lynching Bellatrix, but the mafia godfather is dead. this is a very very good thing.