People who want the best of all possible criminal justice systems have goals for forensic science. We may understand that they aren't always achievable, but we long for them all the same, and some of us actively work toward them.
We want to feel assured that we are convicting the right person, the one who did it.
We want the innocent to be freed and exonerated (which are not the same thing).
We want to correctly identify the deceased, to find some measure of justice for victims, and to prevent those who harmed them from harming others.
Because we never want to be mistaken in these essentials of justice, we want to believe that our methods of evidence examination are going to deliver the truth. If we have doubts here and there, most of us feel sure that modern science has found at least one method that is perfect: DNA.
We want to feel assured that we are convicting the right person, the one who did it.
We want the innocent to be freed and exonerated (which are not the same thing).
We want to correctly identify the deceased, to find some measure of justice for victims, and to prevent those who harmed them from harming others.
Because we never want to be mistaken in these essentials of justice, we want to believe that our methods of evidence examination are going to deliver the truth. If we have doubts here and there, most of us feel sure that modern science has found at least one method that is perfect: DNA.
DNA is lauded in this way, and it is not uncommon to hear it spoken of as the "gold standard." I cringe every time I hear that.
DNA evidence has much to recommend it over many other types of evidence, but it isn't always useful. For example, although most of us want to believe strangers are more dangerous to us than our loved ones, studies have shown that most murder victims knew their killer. This isn't a matter of Homicide Begins at Home barely edging out the Danger From a Stranger competition --
From 1993 to 2008, among homicides reported to the FBI for which the victim-offender relationship was known, between 21% and 27% of homicides were committed by strangers and between 73% and 79% were committed by offenders known to the victims.
That's from a study by the U.S. Bureau of Justice Statistics, which looked at crime statistics from 1993-2010.
What does that have to do with DNA? We all leave our DNA (and microbes, and more) in the places where we live. For example, a husband's DNA will be present in the home where he murdered his wife. It would be really odd if his DNA wasn't present. Finding his DNA in the home, on the victim, even on the weapon -- especially if it is an object that has been in the home for a while -- does not prove him guilty of anything but living at his own address, touching his wife, and handling objects that belong to him. Not evidence of a crime.
And despite what you've seen in a television drama, in the unlikely event a complete stranger shoots you, the odds of crime scene investigators finding useful amounts of DNA on anything but a bloody shell casing at the scene (and that the blood is the shooter's, not yours) are not great.
DNA is also (at present, anyway) a relatively expensive form of testing.
Ignoring the economics of the criminal justice system is not an option. IMHO we make a tremendous number of utterly asinine, penny wise and pound foolish choices about forensic science budgeting — paying the extremely high costs of continued violence, lengthier and more labor-intensive investigations, wrongful convictions, suffering of victims and families, property damage, public health problems, and other safety issues because we won't properly staff and equip labs, let alone spend much to research forensic science or educate our police, courtroom personnel, and public health workers — but alas, no one has put me in charge of all of that yet. Sadly, there is no line item in a county budget called "all the longterm expense and human misery your dumbass decisions cause" to show how wrongheaded a lab budget cut can be.
Still, costs and limits of applications aside, the forensic use of DNA continues to amaze us, and for good reason. It's a fantastic tool. It has helped us solved cold cases, freed the innocent, helped families learn the fates of missing loved ones, identified kings buried under car parks and given us a feeling of certainty in convictions.
It is that last that becomes problematic, because we should never forget that human beings work at crime scenes and in laboratories. And human beings make mistakes.
Over the years, as certain vulnerabilities became apparent, forensic scientists have worked hard to institute controls for quality, to ensure that mistakes were prevented or caught, not just in DNA testing, but in other areas of forensic science as well. But pressures from police and prosecutors, politics within the criminal justice system, budget cutbacks that do not provide the needed level of quality assurance, and other problems can counter those efforts.
If you'll be at the California Crime Writers Conference next month, I'll be talking about this issue and other matters in my forensic science track session, "The Forensic 25." I hope to see you there (Don Johnson and Beatrice Yorker are also be on the conference faculty.)
But if you can't wait or can't make it there, here are a few stories and website links to help you learn more about the ways DNA can go wrong -- or at least, how the humans who work with it go wrong. This isn't, I'm sorry to say, a complete list:
7) German police hunted a female serial killer whose DNA was found at 40 crime scenes -- "the phatom of Heilbronn," a killer whose DNA had been found at six murder scenes and the scene of one unexplained death, a criminal history covering a period of about 16 years. A killer who turned out not to exist. It was instead a case of contamination -- from the DNA of a woman who worked in a Bavarian factory that made the cotton swabs used to collect samples.
So, as in all human endeavors, striving for perfection in forensic science is admirable -- after all, the consequences have to do with lives and liberty -- provided we remember that humans aren't perfect, and that we remind our city, county, state, and federal legislators that we must provide what is needed to both remedy and safeguard against errors.
