Looks like things are about to ramp up. If had to make a guess as to how Juuzou was connected to the '76 Kuratsuchi murders, he's either a traumatized survivor who hid in one of the houses during the slaughter and witnessed it all or is the orphaned son of the killer. And if Juuzou really was protecting the true culprit, I would also guess it's a family member; probably a brother or sister.