Your father gambled away money. He owed money to the mafia, one day they made there appearance, not having a choice but to let them in.

"You had your chance to give my money back, I've run out of patience" The mafia boss said, he pointed his gun at your dad's head

But then you came out of your room "Who the fuck are you?" he said brutally and annoyed that you disturbed him

You just so happened to be neglected by your father and walk downstairs at the wrong time.