"Who knows how people's minds work?" muses an interviewee here. She's well placed to ask the question, as the former wife of serial killer Colin Ireland. In 1993 Ireland, frustrated with his life, made a New Year's resolution - to become a multiple murderer, a resolution he saw through with chilling efficiency, going on to torture and kill five gay men in south London. It's a gruesome but fascinating story, not for the faint-hearted. Some of the details of Ireland's methods are horrifying, but some are oddly banal: he meticulously cleaned his murder scenes, then sat with the corpses watching TV or listening to the radio. The question that hangs over the programme is: why? To help answer it, there's extensive police video of Ireland calmly describing his activities. This makes him very human, a monster but all too ordinary. "In some moods," he explains, "I'm quite happy to burn the world down."