A guide to the numbers
CONFIRMED VICTIMS The widely accepted body count for each killer. This may be the number for which they were tried and convicted but more often it relates to the numbers later confessed to by the killer in question.
POSSIBLE VICTIMS Serial killers are something of a secretive bunch and therefore they will often have a few skeletons in the closet. Literally, in some cases. This is the number of victims that may possibly be attributable to each killer at the top end of the estimate.
KILLING SPREE This is a number in years. Where it was less than a year, this number will be expressed as a decimal.
VICTIMS PER YEAR This is the confirmed victims of each killer divided by the length of their killing spree in years. This will be rounded up to the nearest whole number, as you can't kill fractions of people. Unless you make daytime television programmes.
SERIAL KILLER INDEX This is a number arrived at by a tally of criteria which are significant in the reign of any serial murderer. These are: fear & commotion (their killing spree continued during the glare of social and media panic); killing children; life sentence; death sentence (this counts as two points as it is also technically a life sentence); cannibalism; necrophilia; cruel & unusual (where the killer used excessive brutality before, during or after death); killing relatives; evading capture; escaping from capture & continued killing; a no gun bonus point (serial killing with a gun is so unimaginative); multiple MOs (where the killer will use various modus operandii in order to evade detection or just for their own selfish ends). This gives a total score out of 12. A really top notch psychopath will most likely score on four or more of these criteria.