The press accounts involving convicted cop killer, Troy Anthony Davis, have been focusing on the fallibility of eyewitness identification. In Davis' case there was no physical evidence and the entire case was built upon eyewitnesses to establish the killer's identity. However, seven of nine eyewitnesses who helped implicate Davis for the murder have since recanted their testimony. Grits for Breakfast has also noted the interest in eyewitness identification problems here.
Please review the original post in this series on eyewitness identification. There we stressed the importance of understanding the dynamics involved in these cases by the criminal defense lawyer. Since I promised to explore the nature of eyewitness testimony, its weaknesses, and how an experienced lawyer can use improper police procedures and expert testimony to discredit the testimony of an eyewitness, let's get to it.
There are many sources of error in eyewitness identification. Any identification results from a complex interaction of witness internal and external memory factors. The internal factors relate to the witness' ability to perceive and accurately remember an event. External factors are outside influences in the identification process itself that lead the witness to select a particular person as the perpetrator of a crime. This week we will explore the internal memory factors that affect eyewitness identification.
The human memory generally consists of 3 phases. First, there is the acquisition phase where the witness perceives the event. Second, there is the retention phase where time elapses before the witness must recall the event. Finally, there is the retrieval phase which occurs when the witness attempts to recall the stored event. Elizabeth F. Loftus, Eyewitness Testimony: Civil and Criminal 10 (3d ed. 1997)
During acquisition there are factors that may influence the witness' perception like their age, gender, influence of drugs or alcohol, witness expectations, stress, fear, weapons focus, duration of the event, and differences in race. See Gary L. Wells & Elizabeth F. Loftus, Eyewitness Memory for People and Events, in Comprehensive Handbook of Psychology 157 (A. Goldstein, ed., 2003)
During the retention phase the memory may be altered through the loss of information (forgetting) or the introduction of new information through media sources, conversations with other witnesses, and leading questions by the police.
Finally, at the retrieval phase the types of questions used to elicit the memory may further impact the witness' recollection. For example, questions which suggest the answer like: "Was the robber tall?" rather than "What height was the robber."
The next installment in this series will focus upon the external memory factors which may influence an eye witness identification. I'll try to get that posted soon.