DALLAS – Experts more or less understand what puts young people at risk for becoming criminals: using drugs, carrying a gun, even just believing that they will die young.

But predicting who will commit murder? Not so easy.

A new study by a University of Texas at Dallas criminologist found that it's nearly impossible to predict which juveniles will become murderers. Only two factors distinguished them from other offenders: lower IQ and a greater exposure to violence.

But even more notable was what the study didn't find. Mental health issues and drug use — two popular narratives to explain crime — didn't predict who would commit homicide.

"It's not always the way people think it is. In fact, with respect to homicide, it's nothing the way people think it is," said Alex Piquero, a UTD criminologist and an author of the study.

Piquero studied about 1,350 serious juvenile offenders and found that 18 had been charged with a homicide. Those offenders had an IQ of about 79, compared with about 85 in the other offenders. They also were more likely to have been exposed to violence, such as witnessing an assault or rape.

"Almost everything else doesn't matter," Piquero said. "You always hear on TV that this person had mental illness or this person had this psychological problem. The world's full of people who have a lot of mental illness or psychological problems, but most of them never commit homicide."

The unpredictability of murder could help explain why they happen, Piquero said. "Our best guess is they are situationally driven," he said. "They are assaults and drug deals gone bad."

Dallas Morning News