Judge in Aurora Case Calls for Use of ‘Truth Serum’— But Does It Work?

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RJ Sangosti / Denver Post via Getty Images

DENVER, CO. - MARCH 12: James E. Holmes appeared in Arapahoe County District Court March, 12, 2013. Holmes, the man accused of unleashing the movie theater massacre seven months ago, was arraigned in court. (Photo By RJ Sangosti/The Denver Post)

If accused Aurora mass shooter James Holmes wants to enter a plea of insanity in the “Batman” movie theater massacre, he will have to agree to narcoanalysis.

That’s the ruling from judge William Sylvester, who made the narcoanalysis— in which defendants are injected with drugs to lower their inhibitions and presumably be more willing to tell the truth about their alleged crimes under questioning by prosecutors — a condition of an insanity plea.

At Holmes’ arraignment on Tuesday, he and his attorneys said they were not ready to enter a plea so Sylvester entered a standard not guilty plea on Holmes’ behalf; Holmes’ attorneys can still enter an insanity plea later, with the judge’s approval.

(MORE: Judge Enters Not Guilty Plea on Behalf of Colorado Shooter)

Experts were surprised by the legal determination that “truth serum” could be required in order for Holmes to use the insanity defense. They say that drugs touted for “narcoanalysis,” which typically include the barbiturates sodium amytal and sodium pentothal, are are not effective  and certainly not reliable enough to meet legal standards of evidence.

“I was floored by it,” says Scott Lilienfeld, professor of psychology at Emory University upon learning of the ruling, “The claim that truth serum is truth serum is no longer taken seriously by anyone in the scientific community to my knowledge.”  Moreover, Colorado is one of the states that apply the “Daubert” standard, in which scientific evidence can be disputed by the defense or prosecution.  It requires that evidence meet certain standards to be admissible.

To pass the Daubert test, truth serum would have to be widely accepted in the scientific community and research literature and its use would have to yield a known error rate, both standards that experts say narcoanalysis does not meet. “In my view, it would not stand up,” says Lilienfeld.

But a former prosecutor, now a law professor at the University of Colorado and defense attorney, Karen Steinhauser, told CBS News that the technique is allowed under Colorado law. However, it is used so rarely she could not find any relevant case law.

“The fantasy of a ‘truth serum’ retains a strong hold on the public imagination,” says David Eagleman, a neuroscientist and director of Baylor College of Medicine’s Initiative on Neuroscience and Law, “But no medicine can guarantee truth-telling. If there were such a thing as a truth serum, a citizen might reasonably ask why our legal system doesn’t always ask defendants to use it. For that matter, why not give it to the lawyers on both sides?  The answer is that the fantasy drug doesn’t exist.”

Eagleman and Lilienfeld both emphasize that the drugs most commonly used in narcoanalysis affect the brain in virtually the same way that alcohol does.

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“[D]rugs such as sodium amytal can yield effects like talkativeness and lowered anxiety — effects not unlike drunkenness,” Eagleman says, “But that doesn’t guarantee an incapacity to lie. Although alcohol sometimes causes secrets to slip, we have all witnessed intoxicated people tell untruths.”  In other words, while there may be some veritas in vino, there’s also a lot of blarney — and it’s often impossible to know the difference.

What’s more, studies found that experts cannot reliably distinguish between a truth and a lie told by people under the influence of barbiturate drugs.  Even worse, the drugs both make people talk more and become more convinced that everything they are saying is correct.

“It’s like a double whammy,” Lilienfeld says, “The danger is that people often become more confident under the effects of [so-called] truth serum.  They’re not only becoming more inaccurate but they are also becoming more confident.”

Some experts suspect that the narcoanalysis was allowed in an attempt to determine Holmes’ mental state at the time of the shooting. So the idea would be to determine whether he was suffering from a psychotic episode, and not necessarily to glean the truth about details of the tragic shooting. Still, using a drug that makes such a person suggestible and talkative won’t reliably induce such a recapitulation — and even if it could, it’s hard to know whether someone’s memory of what they experienced while in a psychotic state could ever be accurate, even if the defendant wanted to tell the whole truth.  “The task is to have coherent clinical picture about state of mind of the defendant at the time of the offense,” says Edward Mulvey, professor of psychiatry at the University of Pittsburgh, “And no drug is going to establish the truth about that.”

MORE: Medicine: Truth Won’t Out (A 1951 TIME story on research showing truth serum doesn’t work)

And that may be why narcoanalysis is rarely used in the legal system, where factual, objective truths are the goal. “Even if some future drug could reliably elicit an inability to lie, it would be of limited use to the legal system,” says Eagleman. “Even when a person says what he believes to be true, the statement can still be factually incorrect.”