by Seth Augenstein – Senior Science Writer –
A series of academic studies in Europe and elsewhere have seemed to indicate that killers don’t necessarily go on to kill again.
But a new study of Florida men behind bars for 1st-degree murder makes a clear statistical correlation: murderers have a significantly higher likelihood of killing again, according to a new study in the journal Forensic Science International: Synergy.
The implications for the thousands of unsolved cold cases in America is clear: look at those who have already tried their hand at killing, write the authors, from Iowa State University.
“The United States is in midst of an emerging justice paradigm where cold cases—often decades old—are being solved with the proliferation of genetic data that are publicly available,” write the authors. “A non-trivial number of these offenders had 1st-degree murder arrests or convictions in their offending history … the current study indicates this type of criminal activity has rich criminological forensic value.”
The statistical analysis included 682 male convicted felons incarcerated by the Florida Department of Corrections as of 2013, selected for the study using filters for “murder” and “other violent crime” as part of a larger academic study.
The inmate population was selected, and the raw criminal data only included offenses within the state of Florida—and therefore did not include criminal career data, such as that from the National Crime Information Center.
Of the 682 Florida men, more than 61 percent did not have a homicide for their instant offense. Twenty-six percent were convicted of one homicide, 7.2 percent of two, 2.8 percent of three, and 1.6 percent of four homicides. One offender was convicted of five killings, another inmate of seven, and another prisoner of eight homicides.
Covariates established were prior violent crimes, prior weapons use, armed rape, among others—including two demographic covariates used for the African-American race category.
Negative binomial regression models, and logistic regression models, were used to determine whether the killers were likely to have killed before.
Despite criminal careers progressing in “intermittent and unpredictable ways,” the correlation was clear: killers kill again.
“The current findings are supportive of work that has demonstrated continuity in homicide offending,” write the two sociologists, and a forensic science graduate student. “In six of the nine regression models, prior 1st-degree murder was significantly associated with current homicide offending, and a seventh association was nearly significant.
“Moreover, prior 1st-degree murder was significant for all specification of multiple homicide offending and conferred 185 percent, 198 percent, and 198 percent increased odds across models,” they add. “Statistically and substantively, these are large effects.”
Armed rape was another serious offense correlation. Prior crimes of this type brought with them as much as 725 percent increased odds of killing later, according to the stats.
The previous “striking paucity” of research on murder recidivism included a study of Finnish killers published in 1996 which found that of 1089 killers, “just 36 offenders” killed again. Another was a 2007 study of 336 convicted murderers sentenced to the New Jersey Department of Corrections system between 1990 and 2000; the follow-ups taken after 5 years found criminal recidivism, but zero further homicides.
But the latest study finds that whatever the psychiatric conditions or troubled upbringing, killers tend to kill way more than non-killers.
“In the negative binomial regression model where multiple counts of homicide convictions were considered, and in the logistic regression model where multiple homicide offending was the outcome variable, prior 1st-degree murder convictions were always significant,” they write (author’s italics). “In other words, as the dependent variable evidenced greater extremity in the magnitude of violence, prior 1st-degree murder convictions became more salient.”
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