In a way it is remarkable that DNA evidence has come to be so widely accepted and trusted to the extent that it has. In the beginning, jurors were highly sceptical of genetic evidence. They distrusted it because they didn’t understand the science behind it, and because it dealt with statistics rather than solid facts. They found it hard to believe that a microscopic speck of tissue could be unequivocally identified as having come from a particular person. Defense lawyers took advantage of jurors’ lack of scientific knowledge to cast doubt on the reliability of DNA matches, and many criminals were acquitted despite there being what would now be considered overwhelming DNA evidence of their guilt.

In fact DNA evidence falls a long way short of the hype that surrounds it. To get an idea of how weak DNA evidence really is, imagine what would happen if the criminal fraternity figured out a way to transfer fingerprints from one place to another, or from one object to another, as easily as a person’s DNA can be transferred. A defense lawyer would only have to point out that the prints offered in evidence might have been deliberately planted for a case to be dismissed, or at least for that particular evidence to be thrown out. And yet this is precisely the current situation with DNA evidence. It is automatically assumed that the sample being offered as evidence wasn’t moved or interfered with in any way. If a defense lawyer tries to raise the possibility that their client’s DNA was planted at the scene of a crime in a deliberate attempt to incriminate them, this is usually seen as grasping at straws.