Why should intruder theorists be certain that DNA in the underwear is from the killer and only the killer?

Five of the six scientists and lab technologists who examined DNA evidence in connection with Robert Pickton have admitted to contaminating the evidence.

Not that the evidence was necessarily tainted, but the DNA of several technologists and investigators was recovered on some evidence - one such piece of evidence contaminated was cellophane placed around a revolver found in a trailer on Pickton's farm.

Defence lawyer Peter Schmidt exposed many exhibits tampered by the DNA of investigators showing up, even though there were extensive procedures used by scientists to protect against it.