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We find the defendant....

"We find the defendant...innocent! 
I mean, not guilty!"
If you’ve ever heard the jury foreman give a jury’s decision, you’ll notice that they never say the defendant is “innocent.” Instead, they’ll conclude that the defendant is “not guilty.” Although the terms may sound interchangeable, “not guilty” and “innocent” actually mean two different things. “Not guilty” is a legal conclusion, whereas “innocent” means the person didn’t commit the crime. For example, think of O.J. Simpson. In a court of law, he was found “not guilty” of killing his ex-wife – but if you ask the majority of Americans, they’ll tell you he’s not innocent. Here, we’re going to talk a bit about the distinction between the two conclusions – and why it matters to psychology and law researchers*.

When we say that “not guilty” is a legal decision, we mean that it’s a decision based on criteria described by laws – namely in the U.S., if the prosecutor can convince the jury of the defendant’s guilt. This is based partially on the amount of evidence that points toward the defendant as the perpetrator of the crime, but is not based on this alone. Different levels of crimes have different “burdens of proof” that the prosecutor must meet. For most crimes, this standard is “beyond a reasonable doubt.” Beyond a reasonable doubt is not necessarily quantifiable – it’s not a specific percentage of certainty. It does not mean that a juror has to be completely sure of the defendant’s guilt – just sure to the point where any doubts they have would be unreasonable.

Simpson was found "not guilty" because
the prosecution failed to meet the burden
of proof - that is, convince the jury he did it.

Thus, a prosecutor is trying to win an argument, not just describe the facts. But there are rules for making those arguments, and those rules make up volumes and volumes of legal rules and guidelines, ranging from types of crimes to procedures to what evidence is and is not permissible. Thus, one could cynically say that the legal system is about whether or not the defendant actually committed the crime, but whether or not the prosecutor can prove they did**.

In practice, this means that a defendant can potentially win their case (that is, avoid being found guilty) regardless of whether they committed the crime. It may be that the prosecutor did not present enough evidence to convince the jury – perhaps the only evidence they had was some grainy security footage that may or may not have shown the defendant committing the crime. Perhaps there was reasonable doubt because there were multiple plausible explanations for the physical evidence found at the scene, not all of them implying that the defendant committed the crime.

Another possibility is that a legal rule prevents the defendant from being found guilty – “getting off on a technicality” as they say. This can manifest in a few ways. A trial could be declared a mistrial under some circumstances – such as the jury hearing evidence they should not have. Another way that a defendant could avoid being found guilty based outside of the actual facts of the crime is if evidence is deemed inadmissible. This is particularly relevant for confessions. Say the police did not read the defendant his Miranda rights before beginning an interrogation where the defendant confesses. The judge should not permit that confession to be used as evidence in trial – even if the confession is true – allowing a defendant to go free***.

The law views the process of convicting a person largely as a matter of procedure. That is, the rules are supposed to be followed properly in order for the government to exercise its power to deprive a person of his or her liberty. Failure to meet the standards of the law is grounds for acquitting a defendant. In this system, it’s the job of a defense attorney to make the prosecution satisfy the requirement of establishing guilt beyond a reasonable doubt. This means it’s their job to vigorously cross-examine witnesses, cast doubt on evidence, and call out prosecutors when they act in a way that’s inconsistent with the law (you know, like those dramatic scenes in legal dramas when an attorney shouts, “Objection!”). For better or worse, this means defense attorneys are supposed to do everything legally possible to obtain the best outcome for their client – including an acquittal, if possible – regardless of whether he or she actually committed the crime. It’s a common perception that this kind of work is slimy, but this kind of zealous fighting for their clients is exactly what the adversarial justice system has asked attorneys to do****. The system has no chance of working if they’re not fighting hard.

As researchers working at the intersection of psychology and law, however, we have different somewhat concerns than lawyers. We often care less about the law as procedure and more about whether the law is working the way it’s supposed to –  for example, whether verdicts correspond to whether the defendant actually committed the crime. A lot of our attention is spent on cases in which people who are factually innocent – that is, they didn’t commit the crime – are found guilty.

But how do we know if someone is actually innocent, rather than legally not guilty? We try to determine “ground truth” (that is, what actually happened) with evidence, but that evidence is rarely irrefutable. For example, a person who saw the crime occur can be very helpful – but we know that eyewitness memory can be distorted and inaccurate. We can rely on forensic evidence, but most evidence exists on a spectrum from completely bogus (e.g., bitemarks) to useful, but not scientifically validated and subject to human error (fingerprints). Thus, while there may be so much evidence against a defendant that the jury finds them “guilty”, it’s still possible that the defendant is, in fact, innocent – which is precisely how we end up with wrongful convictions.

Luckily, DNA evidence exists. As the “gold standard of evidence,” DNA identifications are based on scientifically-verified probabilities and are less influenced by human error*****. In certain circumstances, DNA can confirm, or rule out, that the defendant committed the crime. For example, if a victim was attacked and managed to claw the attacker, the police could analyze the skin and blood from under the victim’s fingernails for DNA.
DNA can both pinpoint the guilty, and protect the innocent
If DNA is present and it matches the defendant, that’s extremely strong evidence that the defendant was the attacker. If it’s not a match, however, the police should look for a different suspect – one whose DNA does match.

DNA testing has become a crucial part of criminal investigations since its advent in 1985. Prosecutors present DNA evidence to convict a defendant, and defense teams present DNA non-matches as a way to exonerate their clients. Even after a case is decided (particularly cases that happened in the 80’s or earlier when DNA evidence may have been collected but not tested), DNA evidence can be introduced during appeals or retrials. In this way, DNA evidence has become a very effective way for the courts to try to match “not guilty” verdicts to innocent defendants.

Indeed, some organizations such as the Innocence Project, focus exclusively on using DNA evidence to exonerate the wrongfully convicted by establishing the defendant is factually innocent. If, after conviction, it comes out that there was untested DNA evidence, the Innocence Project may take on the case and lobby for testing. If the DNA from the crime scene does not match the defendant – that is, they are factually innocent, the Innocence Project will then likely get involved in the appeals process to have that defendant released and the verdict overturned. Since their founding in 1992, the Innocence Project has exonerated 356 wrongfully-convicted men and women using DNA evidence.

But what if a case doesn’t have DNA evidence? For a person to be exonerated by DNA evidence, there needs to be DNA evidence that can be conclusively tied to the case. That is, forensics needs to have recovered some source of DNA – blood, skin cells, hairs with the roots still attached, saliva, or semen – from a location essential to the commission of the crime, such as on the body of the victim. After all, if a woman was murdered in their living room and the husband’s skin cells were found on the couch, that does not mean that the husband committed the crime. Thus, the number of cases that have useful DNA cases probably isn’t all that high.

Fortunately, a defendant who has been wrongfully convicted can still be exonerated even without DNA evidence. In these cases, organizations such as the Center for Wrongful Conviction work to exonerate defendants who claim actual innocence as well. Doing this without DNA evidence may be a bit trickier though – after all, evidence that isn’t irrefutable is a bit harder to argue. Defense attorneys will use the facts of the case to argue actual innocence in a variety of ways, such as explaining what errors were made in interpreting the evidence in previous trial or offering evidence that demonstrate the crime was more likely committed by someone else. For example, after being convicted of his parents’ murder in 1990 based primarily on a confession, Marty Tankleff was exonerated in 2007 after his defense team uncovered substantial evidence that Jerry Steuerman (a business parter of Marty’s father) had hired hitmen to murder the Tankleffs. Seeking an exoneration in this manner requires a judge agree with the defense team – which can be difficult.

In fact, just because an error was made does not mean an exoneration is guaranteed. In some cases, the mistake fall under the “harmless error doctrine,” which says that just because a mistake was made does not require a new trial or acquittal. In 1991, the Supreme Court decided that even if a confession was coerced, it can be considered a harmless error1. That is, just because the jury decided guilty after hearing a confession that was obtained by coercing a defendant does not require the defendant be retried or acquitted. Instead, that’s left up to the judge to decide. While this decision may not stand up to logical scrutiny (surely, hearing a confession would affect how the jury’s decision), it falls to a defense team to argue that such mishandling of a confession affected the case. In some cases, the defense is successful – Adrian Thomas, who we mentioned in our post on obedience to authority – was granted a new trial where he was acquitted after the New York Supreme Court decided his coerced confession unfairly led to his original conviction.

For researchers, the importance between “innocent” and “not guilty” is important as well. As we discussed, we sometimes look to real life cases for research ideas. By looking at examples of mistakes in the justice system, we can research why those mistakes happen and try to prevent them from happening again.
"Despite the lack of DNA evidence, no defense
attorney was willing to say, with a straight face,
that the defendant DEFINITELY did not
destroy the teddy bear."
But we like to be sure that these cases are, in fact, mistakes. Although legal research broadly works to improve the legal process (that is, making sure that the rules are fair and fairly applied), we do want to make sure that innocent people are found not guilty and the true perpetrator is found guilty. As such, we like to focus on investigating the cases where we know ground truth – whether the defendant is truly innocent.

This focus has two main benefits. First, we generally do not want to advocate for defendants that committed the crime; if we assume that someone is innocent, but it turns out they are guilty, that can undermine our credibility. As such, it is rare that the research community gets behind a defendant that is not proven factually innocent. Second, if we know ground truth, then we can be confident that something went wrong in that case and investigate the problems. If we know the defendant was wrongfully convicted, we can be confident that at least one mistake was made along the way – and put our time into finding what the mistake was******.

Many of the eyewitness errors that can lead to wrongful convictions have been uncovered in this way. For example, Ronald Cotton (whose case we discussed previously in the context of eyewitness lineups) was exonerated after his DNA did not match the DNA evidence in Jennifer Thompson’s rape kit. Because we know that he was innocent, we are able to go back and look at his case and find ways in which mistakes were made. Cotton’s case offers real-world examples of the types of problems in lineups that can distort eyewitness memory – problems that have been confirmed by empirical research.

Ultimately, we want being innocent to lead to verdicts of “not guilty.” Yet because we are rarely able to know exactly what happened in a crime, combined with human mistakes and biases, an innocent person is not always found “not guilty.” Wrongful convictions, clearly carry personal and society costs, but do provide us the opportunity to learn about, and eventually prevent, the causes of wrongful convictions in the future. By logical requirement, we tend to focus on the cases where we know that the defendant is factually innocent, rather than merely “not guilty,” to study wrongful convictions, which is why DNA evidence has been so helpful in improving psychology and law research and legal practices.

This post was written by Will Crozier and Timothy Luke.


* We’re focusing on the criminal justice system in the United States in this post. Other countries have different systems, some of which have different methods of establishing facts and different possible verdicts.

** Will is sometimes this person, and has said this many times.

*** There are numerous situations in which police are not required to inform suspects of their rights. The case law on Miranda warnings is extensive and complicated.

**** The Radiolab podcast episode “The Buried Bodies Case” covers a case that shows both sides of the potentially “slimy” role of a defense attorney. When Robert Garrow is on trial for murdering hikers whose bodies were never recovered, Garrow’s defense attorney requests a lenient plea deal in exchange for the location of the missing bodies. When the prosecution denied the request, the location of the bodies was never revealed. While some found the defense attorney’s actions reprehensible delaying the hikers’ families closure, others commend the attorney for doing exactly what the adversarial justice system requires – representing his client’s best interest at all times. You can download the episode here

***** The term “gold standard of evidence” was used in a National Academy of Sciences report on forensic science:

National Academy of Sciences. (2009). Strengthening forensic science in the United States: A path forward. Washington, DC: National Academies Press.

DNA isn’t foolproof, though. Complex mixtures of DNA can be difficult to identify, and mishandling of physical evidence can easily render DNA evidence useless.

****** Although a substantial amount of attention is given to wrongful convictions, we also sometimes look to cases in which systems functioned properly or in an exemplary manner. With these kinds of examples, we can attempt to study what went right and provide practitioners with recommendations.


[1] Arizona v. Fulminante, 499 U.S. 279, 111 S. Ct. 1246, 113 L. Ed. 2d 302 (1991).


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