No one will argue that investigating a criminal case isn't hard. Police officers and detectives deal with all manner of people, some of whom have done rather horrible things. The down side of this is it tends to make those officers responsible for keeping the peace and investigating crimes to jaded. Studies have shown that when an officer thinks they have an idea of who the guilty party is they then go after that guilty party, disregarding other potential suspects. The problem is that the officer has to rely on his gut instinct and experience (forensic analysis is not quite as fast as detectives need) and if those same officers in charge of criminal matters have become jaded they are bound to make mistakes.