Predicting who will kill

Another study of killers attempting to build a predictive model doesn't tell us anything we don't know, but does point out by omission that mental illness is not typical of convicted killers.  This doesn't mean that mental issues don't play a role, but that mental issues aren't predictive.  Low IQ and exposure to violence are, as is access to firearms.

Here's the report with a link to the full study in the attribution.
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Criminologists try to solve murder mystery: 
Who will become a killer?

In a study of 1,354 youths charged with serious crimes, the youths
charged with homicide had lower IQs and more exposure to violence.

Predicting which people will commit murder is extremely difficult, according to a study by criminologists at The University of Texas at Dallas.

Dr. Alex Piquero, Ashbel Smith Professor of criminology and co-author of the paper, said he and his fellow researchers were motivated by the lack of scientific literature on distinguishing people who will commit homicide from those who will not.

According to the study, the similarities outweigh the differences between the two groups.

"Based on a whole slew of characteristics that we know predict and differentiate criminal behavior -- a wide variety of criminal behavior: theft, violence, drug use -- can we distinguish from those characteristics the individuals who are charged with a homicide and those who are not?" Piquero said. "We found only five factors that were able to distinguish people who commit homicide from people who don't."

The study, published online in Youth Violence and Juvenile Justice (download the PDF), used data from Pathways to Desistance, a study of 1,354 youths who are charged with serious crimes. The researchers examined how eight demographic characteristics and 35 risk factors distinguished the 18 juveniles charged with homicide from those who were not.

One demographic measure -- age -- and four risk factors were significantly different across the two groups. Homicide offenders had:
  • Significantly lower IQ
  • Higher exposure to violence
  • Higher perceptions of living in a neighborhood characterized by disorder
  • Higher prevalence of gun-carrying
When those five factors were considered simultaneously, only two were statistically significant. The youths charged with homicide had lower IQs and more exposure to violence.

Exposure to violence is measured by how much violence the juveniles report they have seen in their neighborhoods. Piquero said the finding is interesting because research shows homicide is patterned in certain parts of cities.

One belief is that conditions in an environment set the ground rules for what is and is not acceptable, Piquero said. In more disadvantaged, high-violence communities, more crime occurs.

Violence and Serious Theft:
 Development and Prediction
 from Childhood to Adulthood


by Rolf Loeber

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Powell's Books
"For instance, adolescents who are continually exposed to violence in their neighborhoods may learn that it is acceptable to handle their problems through violence," said doctoral criminology student Stephanie M. Cardwell, a co-author of the paper. "If these adolescents find themselves in situations where violence is a possibility, they might take that option because they have learned it is acceptable to do so or that it may be necessary to do so in that context."

Assaults gone bad
Piquero said the results of the study may dispel stereotypes about homicide perpetrators, such as claims they are psychopaths or drug addicts with severe mental illness. In fact, most homicides tend to be "assaults gone bad." They are more driven by situations and emotions than being a product of demographic characteristics, planning or risk factors.

"From a policy perspective and a theory perspective, we shouldn't think about the world as, 'There are homicide offenders, and then there's everybody else,' and we should not try to think about policy programs that are going to prevent people from becoming homicide offenders," Piquero said. "We should be in the business of preventing anti-social behavior, because we do know very well that these risk factors predict all sorts of anti-social behavior."

The project was supported by funds from the Office of Juvenile Justice and Delinquency Prevention, National Institute of Justice, John D. and Catherine T. MacArthur Foundation, William T. Grant Foundation, Robert Wood Johnson Foundation, William Penn Foundation, Centers for Disease Control and Prevention, National Institute on Drug Abuse, Pennsylvania Commission on Crime and Delinquency, and the Arizona Governor's Justice Commission.

Related stories:
Story Source:  Materials provided by University of Texas at Dallas.  M. DeLisi, A. R. Piquero, S. M. Cardwell. The Unpredictability of Murder: Juvenile Homicide in the Pathways to Desistance Study. Youth Violence and Juvenile Justice, 2014

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