DNA Evidence Can Be Fabricated, Scientists Show (2009)

Using some of the same techniques, it may be possible to scavenge anyone’s DNA from a discarded drinking cup or cigarette butt and turn it into a saliva sample that could be submitted to a genetic testing company that measures ancestry or the risk of getting various diseases. One required a real, if tiny, DNA sample, perhaps from a strand of hair or drinking cup. Since red cells do not contain DNA, all of the genetic material in the blood sample was from the man.

Source: www.nytimes.com