Relatively recently, there have been discoveries of substantial genetic links to violent behavior in men with a specific recessive gene, which manifests itself in gang membership, carry/use of a weapon, and aggressive reactions to provocation.
Scientists studying the gene have concluded that those with the variation of the gene are twice as likely to use a weapon in a fight or join a gang, and gangmembers with the gene are strongly correlated with being high-rank, violent members of a gang, with gangmembers with the gene being four times more likely to use a weapon in a fight than other gang members.
Although there is definitely no idea of genetic determinism for peoples' futures being proposed by the scientists, but some of the ways that peoples' bodies react chemically to outside stimuli is somewhat determined. Like anything else, violence is a combination of environmental and biological factors.
If scientists were to ever determine a violent criminal to have a lot of his/her actions very largely a result of genetic predisposition to being more impulsive, do you think they should be treated differently from other criminals?