Recent advances in human genomics have renewed interest in identifying the extent to which genetic variation contributes to antisocial and aggressive behaviours, including criminal acts; alongside this, the debate about how such scientific findings could affect criminal law and potentially mitigate criminal responsibility has re-emerged. However, the heritability of impulsive aggression and antisocial criminal behaviours is far from established, and there is little evidence to suggest that a genetic predisposition toward aggression and/or violence should mitigate moral or legal liability during criminal sentencing. There is thus a danger that any (even partial) attribution of biological causes to criminal acts will be misinterpreted as reductionist determinism. It is imperative that simplistic causal relationships between genetic variants and aggressive or violent behaviour are avoided. Genetic susceptibility is probabilistic in nature: there are no such things as ’criminal genes’, but rather there appear to be common genetic variants that interact with other biological and environmental exposures to potentially increase or decrease risk for impulsive, aggressive, or violent behaviours. In parallel, complex ethical dilemmas regarding the use of genomic data housed in both medical and forensic DNA biobanks for use in criminal proceedings continue to be debated in this era of big data.