AN American website called the Murder Accountability Project (MAP) now offers free and open access to all data on more than 630,000 recorded murders in the US, solved or unsolved, over the last 30 years. Currently, 222,000 murders remain unsolved. Members of the public can try to solve cold cases and work out whether there is a serial killer targeting a specific community or active in a particular locality. The database on offer by MAP is vast, and includes categories such as age and gender of victim, method of killing or weapons used, timeline of murder and the geographical area where the crime was committed. From the intense interest in, and popularity of programmes such as Making A Murderer (Netflix) and the stunningly successful podcast series, Serial, there is strong evidence that the amateur sleuth is alive and kicking. It seems everybody wants to get inside the mind of a psychopath.

But why are we so interested in the psychopathology of "monster killers" such as Ted Bundy, Fred and Rosemary West and, more recently, Stephen Port, who was sentenced to life imprisonment last November for killing four young men in his flat in Essex?

Just as we are captivated by superheroes when we are children – their super-human powers, their ability to defy earthly morality as well as gravity, the triumph of good over evil – we are also captivated by the anti-heroes, those individuals who allow their primitive instincts to run amok, to kill innocents randomly and at will, unfettered by conscience.

The psychopath has no shame and does not experience feelings of remorse or guilt. Psychopaths who kill are callous, detached and feel no empathy for their victims. They often kill repeatedly, over an extended period of time, sometimes years. The psychopath doesn't lie awake at night worrying about a build-up of bad karma or concerned and anxious for the welfare of others.

But this is perhaps one of the very reasons that we are so fascinated by them: maybe there's a bit in all of us that wishes we didn't care so much about others or what they think of us. Maybe there's a bit in all of us that secretly, unconsciously longs to do whatever we like, regardless of the consequences? This is not to say that we are envious of, or aspire to be psychopaths, but more that they stimulate a part of our imagination and primitive instincts that have long been suppressed and, fortunately, kept in check by society and the rule of law. In absorbing the dark details about the modus operandi of psycho-killers, we feel horror but not terror (because we are not victims but bystanders). In this sense, we are safe, we are the ones that got away and this gives us the feeling that we can control the uncontrollable, predict the unpredictable. When we read or watch films about psychopaths, we are not the hunted, but the survivors who live to tell the tale. We can be terrified from the comfort of our own sofas.

The juxtaposition of the apparent "hyper-normality" with the monstrous interior of the psychopathic mind is frightening but intriguing. How can someone seem so normal, so much like "one of us" and yet harbour such awful secrets? Our fascination fixes not so much on their hideous abnormality, but on their seemingly ordinary façade and the fact that they are highly accomplished role players. Psychopaths can be charming, socially adept and intelligent. They are chameleons who change colour to blend in to any social setting. They are hard to spot. You could say it takes one to know one (as we saw in the recent BBC series The Fall, where the detective doing the hunting is as emotionally damaged as the serial killer being hunted).

From the Middle Ages (up until the early part of the 20th century), many communities had "sin-eaters" whose job was to ease the passage of the deceased to heaven by eating a piece of bread laid out on the chest of the person who had just died. By ingesting the bread, the sin-eater would absorb all their sins, thus ensuring a quick and efficient despatch to the afterlife and preventing them from hanging around to haunt the living.

Sin-eaters were normally outcasts from the community and seen as jinxed, sinister and contaminated. In a similar way, the psycho-killer is a sponge for our wildest, cruellest and most primitive imaginings. Once our fears are soaked up in their psyche, we can sleep on the right side of our own wee beds, safe in the knowledge that justice always wins out in the end. Until the sequel gets released.