The adolescent brain defense: The Tsarnaev death sentence and beyond

This is our third and final post on the adolescent brain defense in the trial of the surviving Boston Marathon bomber.

Last Friday, Dzohkar Tsarnaev was sentenced to death on six of 17 capital counts. The immature teen brain was mentioned in the closing summary presented by the defense. From the perspective of sound science in the courtroom, the teen brain defense in the Boston bomber case was feeble. Nevertheless, it is part of a larger project of criminal justice reform that invokes mechanical explanation of brain function in the service of exculpation of blame or mitigation of guilt.

Some prominent neuroscientists appear to long for a "shift from blame to biology." They claim that human beings are victims of neuronal circumstances. This would mean that punishment, let alone the death penalty, would be invalidated as both a concept and practice because criminals do not choose their bad behavior freely. According to Stanford biologist Robert Sapolsky, "Our growing knowledge about the brain makes the notions of volition, culpability, and, ultimately, the very premise of the criminal justice system, deeply suspect."

Neuroscientist David Eagleman of Baylor College of Medicine welcomes a time when "we may someday find that many types of bad behavior have a basic biological explanation [and] eventually think about bad decision making in the same way we think about any physical process, such as diabetes or lung disease." As this comes to pass, he predicts, "more juries will place defendants on the not-blameworthy side of the line."

But is this the correct conclusion to draw from neuroscientific data? After all, if every behavior is eventually traceable to detectable correlates of brain activity—which, we suspect, may be possible at some point in the distant future—does this mean we can one day write off all criminal behavior on a don't-blame-me-blame-my-brain theory of crime?

We doubt it. We agree with University of Pennsylvania law professor Stephen Morse that as long as an actor's values and beliefs are causally relevant to his or her actions, then moral agency exists in the ordinary sense. If people can step back from competing desires, make a reasoned decision among them, and act on the basis of that decision, they possess capacities sufficient for holding them morally accountable—both within the common sense realm of human interaction and under the law.

This is not to deny, in other words, that some murderers have something wrong with their brains. But unless neuroscience can show that a killer was unable to reason and respond to reason or to control himself, it will not succeed as a path toward exculpation. Nor, from a sound-science perspective, should it be used to mitigate because, at this phase of our knowledge, functional brain imaging cannot tell us anything about criminal responsibility that conventional methods cannot already provide.

What's more, are we, as humans, even capable of giving up on—or substantially modifying—our intuitions about retribution?

We are skeptical. Humans' innate sense of justice is deep. Given its manifestation across diverse cultures as well as in children as young as one year old, justice—and punishment—may well be evolutionary imperatives.

One key purpose of punishment is to make perpetrators suffer in proportion to the harm that they have caused the victim and society. When retribution is applied in the real world, it carries great practical value, too.

For one thing, it strengthens citizens' shared norms of moral obligation to one another. Boston Police Commissioner William Evans expressed this view when he said, "I think we sent a strong message that we're not going to tolerate terrorism. They're not going to blow up our Marathon, they're not going to blow up our city, we're not going to tolerate terrorism in our country, and that's the strong message we sent here today."

One of those norms is that victims should be valued as human beings. Consider the following vignette that we use in our recent book, "Brainwashed": A serial rapist, John, attacks Mary, is found guilty, and is sent to prison. A few months later, John is treated with "Castrex," a fictional new anti-rape medication guaranteed to permanently eradicate sexually aggressive urges.

Castrex works after just a few doses, and several weeks later, John is freed. He is no longer a danger to anyone. His rehabilitation was a success. But John's light punishment would have woeful repercussions for Mary, her family, and the community at large.

When society fails to condemn aggressors or simply slaps them on the wrist, victims may feel unavenged and therefore devalued and dishonored. If perpetrators die before they can be judged or are killed in prison before they can be adequately punished, victims and their families may understandably feel enraged. Criminals who do not "pay their debt" can spur victims and their families to contemplate vigilantism and sometimes even undertake it.

Contrary to common perception, such feelings do not always arise out of a sense of vengeful bloodlust. The motivation to punish wrongdoers can instead be motivated by grief or by a solemn sense of duty to set things right. Indeed, many of the Boston jurors were tearful and shaken after delivering their verdict.

Communities, too, resist what they perceive to be inadequate punishment. Consider, as we did in "Brainwashed," the 2011 trial of Casey Anthony, the twenty-five-year-old Florida woman who never reported her two-year-old daughter missing. Widely believed to have killed her child or at least abetted in her death, Anthony received death threats after she was exonerated for murder.

Likewise, jurists often speak of their moral duty to satisfy the victims and their families. When a U.S. district court judge sentenced disgraced New York City financier Bernard Madoff, who swindled thousands of investors of billions of dollars, to a term of 150 years, he explained to the press that the exceptionally long sentence for an elderly man who would probably die within a decade or so was a symbolic way to help the victims heal.

Beyond victims, the legal system itself suffers when criminals are not punished, although not just any punishment will do. The penalty must seem proportionate to the offense. In a system perceived as unfair, juries may ignore judges' instructions, and police officers may impose their own judgment on whether to arrest or abuse suspects or to trump up charges against them. For their part, witnesses may refuse to participate in investigations or to testify. Jurors are more susceptible to nullification—that is, to acquitting defendants who are legally guilty—when the verdict dictated by law is contrary to their sense of justice, morality, or fairness.

Also, victims need to be heard. And surely they were in the Boston Bomber trial. More generally, the idea of a victim impact statement was developed so that the sentencing judge could hear directly about the anguish suffered by victims and their loved ones. Sometimes victims want an apology from their violators—not in place of a penalty, but in addition to it.

Here is where Tsarnaev, who showed minimal remorse, may well have sealed his fate. He generally remained aloof, stony-faced, and passive throughout hours of victim testimony, including the exhibition of many photos of gruesome blast injuries. On occasion, he was observed smiling with his lawyers and appeared to have flashed an obscene hand gesture at a surveillance camera.

In the end, most of the jurors were not persuaded by the idea that Tsarnaev's late brother manipulated him into placing a live bomb. It would be interesting to know if the few who did believe that Tsarnaev was pressured were themselves swayed by the neuroscientist's testimony. Ultimately, the psychological narrative of a young, committed terrorist prevailed.