By Nicole Findlay
The absence crime scene DNA can allow a case to grow cold, a victim to remain unavenged and a criminal to walk free.
To solve crimes where no physical evidence exists, police use behavioural linkage analysis (BLA) to determine, on the basis of crime scene behaviour, whether multiple crimes were committed by the same offender. BLA, a prerequisite to other investigative tools such as criminal and geographic profiling, is still in its infancy. Tamara Melnyk, a doctoral student in forensic psychology spent a year and a half in her MA researching the methodology to test its viability for future police work.
Melnyk examined serial crimes that included sexual assault, homicide and burglary. When she began her research, she anticipated it would be more difficult to find high levels of behavioural similarity between violent crimes because each crime would involve a different victim, who might in turn react differently and affect the perpetrator’s behaviour.
However, despite the presence of a victim, she found the behaviours of these offenders to be extremely similar from crime scene to crime scene.
“One possible explanation for this finding may be that the crime scene behaviour of violent offenders is often guided by very well-rehearsed, fantasy-based scripts,” said Melnyk. Indeed, some rapists and murderers have been known to rehearse their crimes before committing them. This can involve them running though possible scenarios and preparing for reactions a victim might have. In addition to confirming that a criminal’s behaviour appears consistent across their crimes, Melnyk’s research showed that it is in fact possible, even in the absence of physical evidence, to accurately link crimes committed by the same offender based on behaviour patterns alone, especially in cases of serial homicide.
Melnyk is now working on her PhD dissertation. “My goal is to develop a highly accurate, user-friendly, crime linkage tool for police investigators.”
Society may not be able to prevent all crimes, but it can improve the chances of catching serial criminals before they rack up more victims.