Re: "has never had a system where evidence...
You are right. He is wrong. There have always been many situations where some kind of evidence is totally impervious to detection.
That one too. To put it bluntly, the police (and the DA) win ONLY if the criminal has made a mistake. Impervious methods for the concealment and destruction of evidence have been known for 20k+ years.
Sometimes, what is not a mistake today becomes a mistake as new technology is discovered, but that is an exception which proves the rule which is that "To err is human".
The good DA should concentrate on cracking cases traditionally by looking where did the suspect make a mistake (humans always do), instead of wasting all of his energy on the impossible.
Biting the hand that feeds IT
