If you've watched a lot of true crime documentaries, you might ask 'how could no one realise that they were living next door to someone like that?'
We speak to James (find him on Twitter @flatearthaddict), who grew up just a few streets away from Dennis Nilsen in North London, and can answer just how murderers can operate in plain sight.
Scotsman Nilsen admitted to murdering at least 15 men before he was apprehended on February 9 1983, and until Dr. Shipman, was the UK's most prolific serial killer.
He was caught after his neighbours complained of drain problems... and plumbers found a mass of human flesh and bones.
To get rid of his victims, he had dissected them, boiled them up and flushed their remains down the toilet.
This audio programme also includes soundbites from Dennis himself explaining his despicable actions, and gruesome quotes from news reports from the time of his arrest.