What lies beneath?

It apparently takes but a few seconds for people to decide what they feel about a stranger.  Could this be an accurate judgement?  I am not so sure.  Some people use instinct exclusively and accurately, but a pleasant, charming, yet dangerous stranger could pull the wool over many eyes.  There are often accounts from people who have discovered that their neighbour, after many years of living quietly nextdoor, has been arrested for a heinous crime saying, "I can't believe it, he was so charming" or "It couldn't have been her, she always gave the kids sweets."  Most of us like to believe in the goodness of others, we prefer to trust and feel bad if we don't because something doesn't feel right.  After all, criminals are people and look like everyone else.  There are traits that set them apart physically, but they are subtle and can only be spotted by a trained eye.  Some crimes happen through need caused by poverty, but other crimes are seemingly unfathomable.  Words such as evil, psychopath are said in horrified tones.  My question is are murderers actually that different to you and I?  What lies beneath to cause them to behave in a manner that most apparently normal people find so abhorrent?  Could it be psychology, a genetic trait or simply something they enjoy doing, like we enjoy chocolate?  Killing other humans is wrong in the eyes of the law and humanity, but what if it weren't?  Would we see an increase?  People seem to enjoy the sport of hunting.  Shooting and killing a giant, beautiful, defenceless beast such as an elephant is seen by some as an achievement that brings the hunter joy.  I personally feel it is wrong to kill any living thing, even ants are safe in my house! Perpetrators of murder, once arrested, often show remorse, but maybe that is because they were caught. Others show nothing and this is a source of comment because it goes against what should be. I believe that some serial killers have asked to be locked away because they simply could not control their urges. Does this bloodlust or power over life and death or whatever it is they experience become an addiction like a drug or mundanely, chocolate? Is it possible that every person has the potential for murder, but the switch has not tripped, perhaps like some people have inexplicable abilities in other areas? Typical serial killers often have similar traits such as being quiet, socially awkward, yet often charming, loners. People accept that they are a little different and are slightly wary, but never dream that behind the smile is a mind bent on murder. After all many people have these traits, don't they.