Murder by the Numbers

America seems to have the most serial killers, although Russia produced Andrei Chikatilo, the "Rostov Ripper," in the 1980s. Mathematicians discovered that his murders followed the same mathematical pattern as earthquakes, avalanches and stock market crashes. Could serial killers be motivated by math?

Engineers Mikhail Simkin and Vwani Roychowdhury noticed that alhough Chikatilo sometimes went nearly three years without committing murder, on other occasions, he went just three days. They found that the seemingly random spacing of his murders followed a mathematical formula known as a power law.

In LiveScience.com, Natalie Wolchover writes, "When the number of days between Chikatilo’s murders is plotted against the number of times he waited that number of days, the relationship forms a near-straight line on a type of graph called a log-log plot. It’s the same result scientists get when they plot the magnitude of earthquakes against the number of times each magnitude has occurred–and the same goes for a variety of natural phenomena. The power law outcome suggests that there was an underlying natural process driving the serial killer’s behavior." It’s the same type of effect that causes epileptics to have seizures.

Wolchover quotes the researchers as saying that the psychotic effects that lead a serial killer to commit murder "arise from simultaneous firing of large number of neurons in the brain."

In the brain, the firing of a single neuron can trigger the firing of thousands more, each of which in turn can trigger thousands more. Most of the time, this cascade is small and quickly dies down, but occasionally, after time intervals determined by the power law, the neuronal activity surpasses a threshold. In epileptics, that can trigger a seizure. In serial killers, a murder?

Knowing this mathematical formula could help police who are tracking a serial killer to figure out when he may attack next, so they can be prepared, by putting extra patrols in areas where he has attacked before and by telling potentially victims to stay indoors during those days (the "Son of Sam" serial killer, who struck in New York in the 1970s, targeted women with long hair, prompting police to issue a special warning and causing many women to cut their hair). However, it doesn’t help find a "cure" for the killer.

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