If you had a mass-murderer living next door to you, you wouldn't know. The neighbours never do, do they? "He seemed so perfectly normal, although with hindsight he did sometimes leave his milk out on the step until eleven, even on summer days, so there was something unsettling."
But if you did, by chance, happen to spot your neighbour killing people to death, you'd probably call the police. Unless you're like Cam'Ron, of course, whose confused sense of right and wrong means that he'd be putting in a call to Location, Location, Location rather than Crimewatch:
Thank god it's only a hypothetical question, eh? It's charming to see Cam'ron's sense of civic duty and natural justice is easily outweighed by some sort of desire to keep to a muddled-headed 'no snitching' rule. Like so many supposed grown-ups, he seems completely unfit to live in a world where life isn't actually some big stupid team game.
Of course, he'd have to mention the serial killer in his Homesellers Information Pack, so he won't ever be able to get a buyer for 4F.