A serial killer is a type of murderer, characterised by a pattern of homicides that are carried out over a period of time with a 'cooling off' period in between. Three such crimes qualify a murderer for serial killer status.
Such men - for these murderers are most often men - generally fall into two distinct types:
The Disorganised Type - generally suffering from some form of easily diagnosed mental illness (such as schizophrenia) will most often act spontaneously as an opportunity presents itself, and will use whatever is at hand to commit the crime; a rock, a tree-branch, etc... Little or no planning has gone into the crime and there will be little in the way of covering up afterwards. Most often such a man will run from the scene, which will be quite close to where he - or his family - lives.
The Organised Type - the most dangerous serial killer is the one who has planned his crimes well in advance. He has prepared a 'rape-kit' and is ready to strike only when he has found the right victim. The organised type will be well capable of dealing with people, disarming them with his wit and intelligence; he will lure his victims to a place where he can do what he wants - often he may be sadistic and will torture those he kills before he despatches them.