A surprising number of people unfairly accused of crimes will falsely confess to those crimes. The innocent people may be coerced into confessing, or they may simply be confused. As I reported earlier, they may even confess just to get out of the interrogation room. Unfortunately, for them, false confessions are often corroborated with otherwise poor or even fallacious evidence.
According to Saul Kassin from John Jay College of Criminal Justice, Daniel Bogart of the University of California, Irvine, and Jacqueline Kerner of Nova Southeastern University, possessing a confession can lead to a perfect storm of invalid evidence collection. Upon obtaining a confession, law enforcement officers begin amassing evidence that corroborates that confession and discarding disconfirming evidence.
This is not to say that officers of the law are deliberately trying to convict innocent people. It’s just that once they have a confession, they naturally place more credence on eyewitness accounts that place their suspect at the scene of the crime and less on evidence that contradicts the confession. In other words, the gathering of corroborating evidence may be corrupted by the very existence of the confession.
What can be done to ensure that the guilty are punished and the innocent go free? It’s clear that confessions and eyewitness accounts should be considered of secondary importance compared to forensic evidence (fingerprints, DNA, etc). But even more importantly, the people collecting that forensic evidence can't know who has or hasn't confessed. Each piece of evidence must be evaluated independently in order to eliminate preconceived biases.