Normally, when eyewitness identification is excluded for due process violations, it involves police misconduct. For example, police sometimes make picking the suspect out of a line-up unnecessarily easy. If the suspect is a tall and skinny black male, the line-up may consist of white males and heavy-weight black males; picking out the suspect becomes extremely easy for the witness regardless of whether they actually recognize the suspect.
Both parties in Perry's case agree that there was no police misconduct in this situation. However, the witness' identification was highly suggestive since her only option was a tall black man standing next to a police officer. Perry argues that the purpose of excluding highly unreliable evidence at trial is to preserve evidentiary integrity, not to deter police conduct. Based on this argument, whether there is police misconduct should be immaterial.
Given that argument, the future ruling of the Supreme Court may seem pretty clear. The problem, however, is that a favorable ruling for Perry would call into question tons of evidence that has previously been introduced in many trials. If the government violates the defendant's due process rights just by admitting unreliable evidence, then an increased number government witnesses will be barred from testifying.
Many witnesses for the government are not just innocent bystanders to a crime. It is not uncommon for a co-defendant to testify against the defendant at hopes for receiving a lenient plea agreement. Does the fact that the co-defendant may have an incentive to testify for the government make this testimony unreliable? Maybe. Should the fact that it may be unreliable warrant its exclusion? I'm not sure it should go that far. It is the job of the jury to weigh the evidence in order to determine the correct verdict. Instead of taking that job away from the jury entirely, a possible solution might be to educate the jury to the general unreliability of eyewitness testimony. With more knowledge of the potential for unreliable eyewitness identification, the jury may be able to make a more informed decision when deciding whether to give credit to the testimony.
This will no doubt be an important issue before the Supreme Court, and we will continue to watch its progress.