Evidence

Direct Evidence

As the first person called to the crime scene, the police officer is often the most important factor in determining the availability, quantity, and quality of direct evidence. Few officers actually observe the crime in progress, so it is the police's function to gather information and statements from witnesses through a process of interview and interrogation as quickly and thoroughly as possible.

In the late 1990s, research psychologists presented new theories of flawed perception by eyewitnesses, proving that at least 50% of subjects in observational experiments failed to perceive very major things right in front of their eyes. This phenomenon, dubbed “inattentional blindness,” brought new understanding to the concept of “change blindness,” where people often fail to detect changes in their field of vision during eye movement or other interruptions.

In 1999, Harvard psychologist Daniel Simons updated these phenomena in an experiment where subjects watched a video of two groups of people dressed in black and white passing a basketball between players. Instructed to count the number of passes by the white team, 50% of subjects insisted they never saw the gorilla (a person in a gorilla costume) walk directly into the field of play. Simons's conclusion, called “selective looking,” suggested that individualistic variables of both the scene and the observer can raise critical issues about the credibility and accuracy of human eyewitness testimony.

Historically, sketches, diagrams, and photographs were used to record the observations of witnesses and investigators in an effort to minimize the possibility of human error or faulty memory. Still, there are cases where photographic evidence has only contributed to a controversial crime as it is scrutinized by experts with different opinions. The famous Zapruder film of the assassination of[Page 179] President John F. Kennedy in 1963 has divided experts and spawned numerous theories as to the number of gunmen and shots fired. A photograph of the assumed shooter, Lee Harvey Oswald, bearing a rifle similar to the type used in the assassination, was widely cited as evidence of his culpability as the lone shooter, but it has been rejected by many as a fake composite of several photographs. More than 40 years after the event, forensic experts continue to disagree about the Warren Commission findings of a single “magic” bullet theory, while eyewitnesses—such as Nellie Connolly, who sat in the car with President Kennedy—continue to insist that more than one shot was fired.

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