Just waiting for the illegitimate relative to turn up!

How can anyone else be strong enough or old enough to be the SBK? Would not be surprised if the mother thought the relative dead but never saw the corpse and too ashamed to tell the police even though her children are injured or dying around her by the end! Thats one guess anyway! Anyone got a better plan?

Anyone who still has faith in humanity has never been to the imdb boards.