Severe destruction of DNA can be tested by:

PCR is an in vitro method for amplifying a selected DNA sequence that does not rely on the biologic (in vivo) cloning method.  PCR permits the synthesis of millions of copies of a specific nucleotide sequence in a few hours.  It can amplify the sequence, even when the targeted sequence makes up less than one part in a million of the total initial sample.  The method can be used to amplify DNA sequences from any source, including viral, bacterial, plant, or animal. Key concept: Polymerase chain reaction can even find cases with severe destruction of DNA.  Ref : Lippincott’s illustrated reviews for biochemistry , 7th edition.