An Educational Guide to Forensic Psychology in Criminal Justice

The criminal justice system calls on expertise from various fields, including psychology. Forensic psychology, as defined by the American Psychological Association, is the application of clinical psychology to legal cases, which can influence whether a defendant is found guilty as well as the potential sentence that may be imposed. Psychologists may do threat assessments for schools or other organizations or evaluations in cases of child custody. They may determine if a defendant is mentally capable of standing trial. Forensic psychologists are also involved in screening and selecting applicants during the hiring process for law enforcement positions.

A question often asked when a crime is committed is, “why?” Psychology has been used to help answer that question by looking at the psychological elements within a person that drives their behavior. Examining people’s motives has become a critical part of criminal trials since the dawn of forensic psychology as a specialization.

Wilhelm Wundt founded the first psychology lab in history in 1879, but some of the earliest research on psychology in legal testimony was done by James McKeen Cattell at Columbia University. Cattell asked student subjects a set of questions and would rate their degree of confidence as they answered. What he found was that how confident a student was about their answer had no connection to whether their answer was correct, which called into question the reliability of eyewitness testimony. Brian Joslyn, a Cincinnati criminal lawyer advised this is often the case and something he has experienced to this day.

William Stern built on Cattell’s work in his research, which focused on how well people recall events in emotional situations. He found that heightened emotions could reduce the accuracy of people’s memories, raising further questions about the testimony of witnesses who experienced tense or frightening situations. Stern went on to establish the first applied psychology academic journal.

The work of researcher Alfred Binet has also come into play in the courtroom. Binet studied suggestive questioning, showing how people could be persuaded to remember things that didn’t actually happen. He also developed an intelligence test for children; his work was later revised for use on adults by Lewis Terman at Stanford to create the well-known Stanford-Binet test. This test could be used to help determine whether a person was mentally competent to stand trial. It has also been used to assess applicants for jobs in law enforcement.

The specific use of psychological testimony in the courtroom can be traced back to criminal trials in Europe in 1896. One of the first to provide expert testimony was Albert von Schrenck-Notzing, who testified during a German murder trial about the effects of suggestibility on the testimony of witnesses, pointing out that sensational press coverage before the trial may have influenced witnesses’ memories.

A significant milestone in forensic psychology was the discovery that systolic blood pressure correlated to lying behavior. This work by William Marston led to the invention of the polygraph. His research was also famously influential in the case of Frye v. U.S., in which Marston was set to testify about his examination of the defendant, that supported the defendant’s claim of innocence. His lie detection experiment on the defendant was not admitted in court, but this point was argued before the jury, so they heard the claim that the test had found the defendant innocent. The jury voted to convict but not on the most serious charge, which would have carried the death penalty.

The most significant growth in the field of forensic psychology in the United States came after World War II. Until that time, doctors with medical degrees were seen as far more credible witnesses than psychologists, but as a result of a 1940 case, People v. Hawthorne, the court held that the standard for an expert witness was to be based on the level of knowledge, not on the presence of a medical degree. This ruling came about via a case in Michigan in which the court would not allow the testimony of a credentialed professor of psychology. The court was found to be in error on that decision upon appeal to the Michigan Supreme Court.

Forensic psychologists have been involved in many famous court cases. For instance, the testimony of psychologists was included in 1954’s Brown v. Board of Education, which declared segregation laws unconstitutional. In more recent history, the work of forensic psychologists helped to convict mass murderer John Wayne Gacy Jr. in 1980. Gacy was a serial killer who raped, tortured and murdered at least 33 young men and teenage boys in the 1970s. Gacy tried to mount an insanity defense with a sex crime attorney, but psychologists determined that the sex crimes involved a high degree of premeditation, including detailed plans to hide the bodies of victims. As a result of this work, Gacy was given the death sentence for his crimes.

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