DNA Evidence: too good to be true

With DNA extraction techniques getting more sophisticated by the day questions like Is it possible to test strands from grandma's hair brush? are increasingly being asked.

The answer, which used it be only if there's a root on the strand, is increasingly more nuanced, and always with the rider - at a a price!

With greater capability comes greater probability of contamination.

This article from Nature includes this description of an experiment

"We asked pairs of people to shake hands for two minutes and then each individual handled a separate knife. In 85% of cases, the DNA of the other person was transferred to the knife and profiled. In one-fifth of the samples, the DNA analysis identified this other person as the main or only contributor of DNA to the 'weapon'

Caveat Emptor