misguided entrapment of Colin Stagg during the hunt for the killer of Rachel Nickell.
By contrast, contemporary criminal profiling is more data-driven. More about number crunching and less about the judgment of a single expert. Thousands of criminal records are pored over to look for factual correlations that could usefully inform investigations. It's been shown for example, that two burglaries closer together geographically, or closer together in time, are more likely to have been committed by the same person.
This empirical approach is also being brought to bear on more psychological aspects of crime scenes. In a new study, Carrie Trojan and Gabrielle Salfati studied a set of criminal records to see if there were links between the crime scene behaviour of murderers and the general theme of their offending history. The majority of murderers in the USA, where this research was conducted, have an existing criminal record, so if such a link could be established it could help guide future murder hunts.
The researchers' prediction was that murder scenes betraying signs of uncontrolled violence and impulsivity, which they labelled as 'hostile', will be more likely to have been perpetrated by a person with a record of committing crimes bearing that same hall-mark, such as assault, domestic violence and vandalism. By contrast, they predicted that murder scenes betraying signs of calculation and an ulterior motive, which they labelled 'cognitive', such as hiding the body, and involving acts of a sexual nature or robbery, will be more likely to have been committed by someone with a criminal record involving more considered, 'instrumental' crimes, such as theft or evasion of arrest.
Trojan and Salfati obtained records from the Cincinnati Police Department of 122 murders committed by someone who'd only ever killed once (between 1997 and 2006), and records of nine serial killers from across the USA. The latter had killed between three and six people each, but only ever one person at a time. The researchers first established that it was possible to classify the majority of murder scenes as either hostile or cognitive based on a scene having twice as many signs of one theme, in proportionate terms, than the other. On this basis, 87 per cent of the murder scenes were considered to have a dominant theme.
Next, the researchers showed that the vast majority (95 per cent) of murders by a one-victim killer were associated with hostile murder scenes. This chimes with the fact that nearly half of all murders in the USA occur during arguments. In contrast, the murder scenes left by serial killers were approximately half the time (51 per cent) hostile themed, and half the time (49 per cent) cognitive themed.
Turning to the key question of whether murder scene behaviour echoes the murderer's criminal history, the results unfortunately became far messier. For murderers with one victim, the most common pattern (26 per cent) was for a hostile crime scene to be left by a person with a history of more instrumental crimes. In other words, there was most often actually a mismatch between murder scene behaviour and offending history. For 24 per cent of single-victim murderers, their was a hostile/hostile match in the murder scene and offending history. For the remainder, the classifications were mixed or unidentifiable.
What about the serial killers? Although the largest category (33 per cent) did show a murder scene/ offending history match - being more cognitive and instrumental in each case - other patterns were also found, with 22 per cent tending to leave a mixture of cognitive and hostile murder scenes, but with an instrumental offending background, and another 22 per cent leaving a mixture of murder scenes and having a mixed background of offending.
'When linking criminal history to crime scene behaviour, thematic consistency was not evident in most cases,' the researchers concluded. 'Essentially, the results show that most single-victim homicide crime scenes display the same theme and that offenders are equally likely to have a pattern of either violence or instrumentality in their criminal background and a decent number have no pattern in their criminal history …' And here's the rub, Trojan and Salfati added: 'It would be difficult to apply this information in investigations.'
The study had its limitations. Not only was the number of serial killers woefully small, but as the researchers themselves concede, they didn't look at the time-line of murderers' past offences. This could have revealed useful patterns, such as that it is a murderer's recent style of offending that is linked to his or her murder scene behaviour, rather than his or her overall career pattern of offending. 'However,' the researchers said, 'because this study was the first to directly focus on the link between criminal history and crime scene actions, it provides an important first step for more in-depth examinations.'
Trojan, C., and Salfati, C. (2011). Linking Criminal History to Crime Scene Behavior in Single-Victim and Serial Homicide: Implications for Offender Profiling Research. Homicide Studies, 15 (1), 3-31 DOI: 10.1177/1088767910397281
Post written by Christian Jarrett (@psych_writer) for the BPS Research Digest.