Ask any of the uncountable convicted rapists and killers who were eventually freed when dna evidence contradicted the eye witness accounts.
There are myriad subtle ways to let potential witnesses know "who" the suspect is. For example, if the suspect has been described as tall, average build, putting him in a line up with a bunch of short, stocky individuals guarantees an I.D. from a shell-shocked witness. We're talking dead police officer here. I'm not the least bit confident that everything leading to the conviction of Troy Davis without a hint of physical evidence was completely without leading and/or coercing their identification, as most of the witnesses have already conceded over the years.
Years ago Detectives had to rely on eye witness' and whatever physical evidence was available...there was no DNA....The investigators gathered everything they could and handed it to the Prosecutors Office and then they were done with it...were mistakes made..absolutely.....fast forward to today.
Dna and technology has changed investigations and has made it possible to prove guilt or innocent with alot more scientific accuracy
I dislike the death penalty, ...but I do believe there are some humans that are not worth salvaging and dont deserve to live 40 yrs on the taxpayers dime.
Ted Bundy....Jeffrey Dahmer....and yes I believe there needs to be firm proof of guilt.