It is well-settled among social scientists who have studied the mechanisms of eyewitness memory that certain police practices are likely to enhance the reliability of identifications resulting from police lineups, whereas certain faulty practices have been demonstrated to diminish that reliability. Yet under federal due process law (i.e. Manson v. Brathwaite), identifications from egregiously flawed police lineups are routinely admitted because the result is found to have an independent source, notwithstanding the suggestivity of the lineup procedure.
Courts have widely interpreted Manson — however wrongly — to mean that it really doesn’t matter how suggestive a procedure is, as long as the witness had, for example, a sufficient opportunity to view the perpetrator such that she would theoretically have been able to ID the person if the police hadn’t gone out of their way to suggest that their suspect was the guy. Under that unfortunate interpretation of the governing rule, due process has been rendered a fundamentally ineffective legal vehicle for challenging the admissibility of suggestive and otherwise unreliable police lineups.
But what about Frye? Here in DC, in order to introduce evidence that flows from a scientific procedure, the proponent of the evidence must show that “the thing from which the deduction is made [is] sufficiently established to have gained general acceptance in the particular field in which it belongs.” A police lineup is a scientific experiment designed to test an eyewitness’s ability to accurately recall the identity of the perpetrator. The community of experts in the field of human memory are in a state of broad consensus with respect to the lineup procedures that make for a reliable test of human memory, and those that make for a poor one. When there is anything short of a consensus among that community — that is, the community of social scientists who have actually researched the effectiveness of the procedures employed by police to test witness memory — with respect to the reliability of a particular procedure, identifications flowing from those unreliable procedures should be excluded from use in criminal trials.
The question before the court in Frye itself was similar, when it was faced with a challenge to the admissibility of the results of a polygraph test. The polygraph is designed to test the accuracy of a person’s account of some event. A police lineup is also designed to test the accuracy of a person’s account of some event, and specifically, the identity of the perpetrator. When a lineup is administered in accordance with settled best practices — i.e. with proper instructions, conducted by someone who does not know the identity of the suspect, with an adequate number of fillers, where the fillers match the characteristics of the original description, with only one suspect per lineup, etc. — then the relevant community of scientists are in consensus that the procedure is more likely to yield an accurate identification. When those procedures are not followed, there is broad consensus for the exact opposite proposition — namely, that the procedure and any identification that flows from it are demonstrably unreliable.
Evidence flowing from an unreliable test of memory should be excluded for the same reasons that the DC Court of Appeals excluded evidence from the polygraph test in 1923: its proponents cannot establish that it reliably produced the evidence it was purported to produce.
So why not use Frye (and, equally, Daubert) to keep out unreliable IDs? It just struck me that you shouldn’t even need due process to keep out the results of a procedure whose unreliability is corroborated by a broad consensus among scientists.