According to Nature magazine, Bayout's defence argued that he was mentally ill at the time of the offence. The court accepted that argument and, although it found Bayout guilty of the crime, imposed on him a reduced prison sentence of nine years and two months.
Bayout nevertheless appealed the judgment, and the Court of Appeal ordered a new psychiatric report. That report showed, among other things, that Bayout had low levels of the neurotransmitter monoamine oxidase A (MAO-A) — an important development given that previous research discovered that men who had low MAO-A levels and who had been abused as children were more likely to be convicted of violent crimes as adults.
Ultimately, the Court of Appeal further reduced Bayout's sentence by a year, with Judge Pier Valerio Reinotti describing the MAO-A evidence as "particularly compelling."
Upon a brief review of the scientific evidence, certain glaring problems with the court's judgment quickly become apparent. Most obviously, the research showing an association between low MAO-A levels and violence tells us nothing about Bayout's — or any specific individual's — propensity for violence. Indeed, while a significant percentage of men with low MAO-A levels commit violent offences, the majority do not.
Yet the fact that the court allowed such evidence to influence its verdict suggests that neuroscience, while not eliminating criminal responsibility, might lead courts to conclude that defendants with certain neurological deficits are less responsible than those with "normal" brains.
There is, in fact, a precedent for this, and it's one that few people question. Adolescents in virtually every country are subject to differential sentencing, and in many cases to an entirely separate system of justice, because their neurobiology renders them less blameworthy, less responsible than adults.
Via Ashish Umre