Expert Witness Testimony in the Boston Bombing Trial

Mental health professionals, like psychologists, neuropsychologists, and psychiatrists, are often consulted in the course of capital criminal trials. It is a popular belief in our society that criminals commonly “get off,” are let out of jail, after raising a mental health defense. In the popular view, a mental health expert comes into court, testifies that the defendant was “insane” at the time of the offense, the jury is swayed, and the defendant is promptly acquitted. In fact, nothing could be further from the truth. For example, in my home state of Tennessee, there have been none – precisely zero – acquittals in contested murder trials due to a finding of insanity in the past 15 years. A colleague of mine has given a talk entitled, “The Insanity Defense: You’ve Got to be Crazy to Use It.”. He’s right.

True insanity cases are vanishingly rare, and even rarer are cases where the claim of insanity works for the defense. In the course of my career, I have evaluated approximately 2,000 offenders, 60 of them on trial for their life. I have also testified that a defendant was insane precisely twice in murder trials. In neither of those cases was the defendant acquitted.

So in the recent Boston Bombing murder trial of Dzhokhar Tsarnaev, why was a neuroscientist asked to testify? Why does it seem that most high-profile cases that grasps national attention – the Vanderbilt rape trial, the Jodie Arias trial, or the upcoming Colorado theatre shooting trial – seem to have a procession of mental health experts who have or will testify on the part of the defense?

The answer, of course, lies in the law. Mental health experts have skills that enable them to address many legal questions besides just the question of whether the defendant was insane at the time of the offense. For example, was the defendant able to understand her Miranda rights before she gave her confession? Was he too drunk to premeditate murder at the time? Does he understand what’s going on well enough to help his attorney defend him? Does he understand that he’s about to be executed because he was convicted of a crime? And perhaps the most frequent question, Are there mitigating circumstances that the court should consider in delivering a sentence?

The latter question is the reason for Dr. Jay Geidd’s testimony in Tsarnaev’s trial this past week. When it comes to capital trials, the law is extremely broad about what kind of potentially mitigating information can be admitted in court for the jury to consider in whether to sentence a person to death.

Federal law essentially throws the door open to almost any conceivably relevant evidence to be admitted in the sentencing phase of a capital murder trial (just as the door is also wide open for the prosecution to introduce “aggravating factors”). The aggravating factors typically introduced by the prosecution usually involve questions of fact. This includes how brutal the murder was, also was a peace officer the target of the crime, did the crime have a terroristic motive, and are usually established without the need for expert testimony.

The defense, on the other hand, is usually more interested in introducing information aimed at reducing the perceived culpability of the defendant. Such as, his immaturity, his intoxication at the time, his history of abuse, his mental health problems, his current remorse for his crimes. And these are topics that are typically best addressed by a behavioral scientist, the psychologist or psychiatrist.

The main thrust of Dr. Geidd’s testimony was the immaturity of Tsarnaev, in fact, of all 19-year-olds. Dr. Geidd is a psychiatrist and neuroimaging expert who works for the National Institutes of Health. Brain research has established that the human brain is not fully developed usually until the age of 24 or 25. We know this by examining the myelination of the nerve tracts in the brain. Myelination is a process that occurs as a person grows up, whereby the nerve cells are coated with myelin, a substance that vastly speeds up the rate of conduction through nerve cells. Therefore it improves brain efficiency and function.

A common neurological disorder, multiple sclerosis, works by destroying the myelin that coats brain cells, causing a person to think less efficiently, to retrieve information more slowly, and to have impairment in vital functions like vision or motor skills. The myelin is easy to visualize on brain scans. Little babies have almost no myelinated nerve tracts in their brains. Adults have thousands of large tracts that are myelinated. However, adolescents are somewhere in between.

We all know the effects of this fact. Insurance rates are higher for adolescent drivers, because they tend to have more accidents. Adolescents tend to be more impulsive and to have poorer judgment. We don’t let adolescents marry without permission, sign contracts, or even vote. Not a week goes by that my 14-year-old son doesn’t comes home talking about a crazy story about aliens or Sasquatch that he’s read from the internet, and believes it as gospel truth. As a society, we recognize that adolescents aren’t as responsible as adults. The Supreme Court, in Roper v. Simmons, 2005, held that individuals 18 years of age and less can’t be executed even if they commit a capital crime. This decision reflects the fact that the Court understood that adolescents aren’t as responsible as adults. Hence they can’t be found as culpable, as adult defendants.

So what do we do with 19-year-old Tsarnaev? If his brain is like that of most 19-year-olds, his nerve tracts are not yet fully myelinated. This puts him at risk for poorer judgment as compared to adults, being unduly influenced by others, having difficulty appreciating the consequences of his actions, and being unduly impulsive. In other words, if he’s like the typical 19-year-old, he still has some growing up to do. Perhaps the adult Tsarnaev would have chosen a different path. Maybe he would have stood firm against his brother’s monstrous plans. Who knows, he might even have turned his brother in. And as time goes on, if he is not executed, he will grow and develop, perhaps to question his actions, perhaps regret them. Just as possibly he might become more hardened and convinced that he did the right thing.

This is the information the jury needs to consider. Do we as a society believe that his actions were so monstrous that they demand the ultimate penalty, without any other considerations? Or do we want the jury to hear all the contributing factors, all the future possibilities, before the awful decision for life or death is made? In the federal courts of America, the law mandates the latter course. I happen to think it’s the right path to follow.