Dr. Vass gave a great talk during his initial testimony in the State's case about all the process the cells go through during decomposition after the body dies. It was really easy to understand but also had a lot of detail and was engaging and interesting!
But the upshot is that the cells are essentially digested (by their own internal chemistry and by bacteria and eventually by exposure to the elements) and so by the time a body is a skeleton, there wouldn't be much/any human cellular DNA left to analyze. Especially in the presence of water and heat. DNA just wouldn't stay intact very long under those conditions.
:twocents: To clarify a "smidge": "touch DNA" is a process that assists in the identification of a DNA pattern from very small samples of an unknown, in lay terms, a few CELLS are used in the "touch" process. "touch" is so called because it takes the shed epithelial cells available from touching, handling, pulling on/off an item, etc. rather than taking cells from the human organism where MORE cells are present & available.
The statement above: "
"so by the time a body is a skeleton, there wouldn't be much/any human cellular DNA left to analyze".....
relates to the possibility of "pulling off" foreign (the perp's) cells (epithelial aka skin) and due to the reasons stated in the second sentence, which are totally correct on "on the money", making the retrieval of
Perpetrator's (or according to Baez, Roy's:floorlaugh

DNA probability totally NIL.
DNA of the VICTIM within the protected celluar material (ie. bone marrow, histiocytes (bone cells), possibly tooth pulp) COULD be isolated and tested via conventional DNA methodology.
Further info (in people language):
http://www.forensicmag.com/article/touch-dna
"THE" company supplying testing "kits" to worldwide agencies (yeah, even the Netherlands):
http://www.bodetech.com/forensic-solutions/dna-technologies/touch-dna/ The link is their description of touch DNA, the entire site is loaded with good info (IMHO), & an agency filled with hard working, nice, smart helpful people!