It is an extremely rare case which is solved by forensics alone. The chief value of forensics is in bluffing out the suspect and getting him to confess.
If the police had everything they need to prove all elements of first degree murder, they would not use interviews or interrogations. Anytime a cop is asking questions, it is because he needs the suspect to hang himself.
The American public is always impressed by novelty and mystery. There are today entire genres of true crime on TV that show off the system’s forensic capabilities.
What goes unmentioned – purposefully – is ….…. that physical and biological evidence is often not present. TV producers have decided to “wing” the American police and to add to their perception of omniscience. You may as well give up now, we know it all.
It is not necessary to “explain” anything to the police. They don’t decide innocence or guilt – the courts do. The opinion of a police officer or homicide detective is irrelevant. Unfortunately, the cops have conned the public into believing that they need to ‘cooperate’ and help solve the case.