We have previously written that, of all the forensic tests currently used in criminal investigations, DNA analysis is by far the most accurate and reliable. But it is important to note that these tests are not foolproof. And as DNA analysis techniques become more and more sophisticated, the risk of error may actually be going up rather than down.
In February, the New York Times ran an article about a promising but controversial method of DNA testing known as "low copy number DNA analysis." It is promising because it allows technicians to extract genetic information from unbelievably small DNA samples. It is controversial from a criminal justice standpoint because the risk for errors is high.
The science of DNA analysis first started in the 1970s. At that time, large amounts of DNA were needed in order for an analysis to be conducted. In the 1980s, a famous biochemist developed a method known as a polymerase chain reaction, which can be thought of as a photocopying machine for DNA samples.
With this advancement, it was possible to extract genetic information from smaller DNA samples. Processes and techniques have been further refined over the past several decades. Now, low copy DNA analysis can produce test results with a sample as small as 10 to 20 molecules.
But because these tests are now so sensitive, they can easily be contaminated by DNA from lab workers, or even from airborne particles in the lab. Moreover, a tiny sample of someone's DNA on an object - a gun handle, for instance - does not constitute proof that the person even touched it, much less used it. Our DNA is transferred to everything we touch, and some of it could be transferred to others who later touch objects that we have touched. By analyzing such small samples, low copy DNA analysis could show that our DNA was found on something which we had no connection to.
This new analysis method could lead to significant breakthroughs in other applications of genetic science. But criminal convictions require proof of guilt beyond a reasonable doubt. At least for now, low copy DNA analysis leaves a lot of room for reasonable doubt.