Pcr makes it possible to the tiniest amount of dna from crime scenes

It multiplies the amount of DNA available.
Explanation:
While it's not necessary to perform Polymerase Chain Reaction (PCR) on every DNA sample found at a crime scene, it is often used by forensic scientists because it amplifies the DNA in vitro. This just means that from the tiny samples that may be found at a crime scene, scientists are able to amplify those and give themselves more to work with in the lab to identify the people involved.