Geographic profiler Kim Rossmo calls crimes such as those committed by Paul Bernardo or the Yorkshire Ripper a "classic needle in your haystack problem."
Early in the investigation into what became known as the "school-girl murders," Bernardo's name was among 3,200 suspects in a case that generated some 31,000 tips.
In the case of the Yorkshire Ripper, who killed 13 women in northern England, there were 268,000 names put forward.
And unlike the images portrayed by Hollywood, "stranger crimes are not easy to solve," Rossmo told an audience gathered Friday at the University of Regina.
The public lecture was held as part of the university's first National Summer Institute for Statistical and GIS Analysis of Crime and Justice Data, which attracted about 45 participants for the week-long classes. (GIS refers to geographic information systems.)
Rossmo, a former Vancouver police officer for 21 years, is a pioneer in crime mapping and geographic profiling, which can help police close in on that proverbial needle in the haystack.
Not only did the criminologist, who is currently a research professor at Texas State University, assist in the Bernardo case, but several high-profile crimes in the U.S. including the Washington snipers.
He's commonly asked how many crimes he's solved by geographic profiling, which he defines as a way of analysing crime locations to determine the most probable area of the offender's residence. His response is none. Rather, it's a tool that can help police focus their investigation.
While most murders are committed by someone known to the victim, a genuine "whodunnit" forces police to cast a wider net, often leading to information overload that geographic profiling can help pare down.
He said a so-called random murder isn't so random if one considers how the offender "hunted" the victim or chose the location to commit the crime.
Using real cases, Rossmo showed his audience maps containing clusters of dots tracking crimes ranging from abductions to murders and rapes.
His computer then shifted to maps that superimpose colors over those dots, with the color becoming more intense the closer to the cluster. Then Rossmo added the known offender's home or office, often in the red zone at the core of the crimes.
"The locations of crimes are very much a function of a criminal's non-criminal behaviour," Rossmo said.
Rossmo noted criminals, like all humans, are creatures of habit, who don't like to stray far from home or known neighbourhoods. For example, Bernardo dumped his first victim in a lake where he and his wife (and co-killer) Karla Homolka used to park when they were dating.
Clifford Olson encountered his victims near his residence, but dumped their bodies near a prison where he once spent time.
"Offenders hunt closer to home than where they dump their bodies," he noted.
But Rossmo cautioned that geographic profiling doesn't "give you an X that marks the spot." Rather, it allows police to prioritize their search or suspects. "It can serve as a useful winnowing tool."