Oh, real-world evidence problems are so messy! Consider the case in which the victim of a homicide - before his death - allegedly identified his killer by blinking his eyes three times. See Lisa Cornwell (AP reporter), Ohioan to appeal conviction in 'dying blinks' case Houston Chronicle (May 17, 2013). One thinks of Stephen Hawking.
There were "mundane" problems in the Ohio murder case.
For example, the paralyzed victim had been treated with drugs. The victim "failed to respond" to some questions. Sometimes it was "unclear" how often the victim blinked. During questioning, the victim was shown only one photograph, a photo of the defendant.
The victim died about two weeks after he was questioned by the police.
Did the blinks amount to a "dying declaration"? (Did he think he was dying, did he think his death was imminent, etc.?)
If they did, were the victim's statements "testimonial" for purposes of contemporary Confrontation Clause jurisprudence? (I hesitate to call it "jurisprudence," but ..., oh well.)
Was the identification procedure so unduly suggestive that it violated the federal constitutional guarantee(s) of Due Process?
But, above all (I think), is this question: Did the jury have sufficient evidence to conclude beyond a reasonable doubt that the defendant was the killer?
Evidence marshaling software MarshalPlan