Is DNA Foolproof? (Part 2)

DNA strand

DNA is one of the most widely used tools in the legal system. As discussed in a previous post, even though many prosecutors rely on it to establish identity in criminal cases, it is still not without its flaws.

For starters, what many prosecutors will not admit is that the DNA of all human beings is almost identical. To be more accurate, scientific studies show that humans share approximately 99.9% of the same DNA, with the remaining 0.1% being what makes us all individuals. It is only the small differences between DNA that distinguishes one person from another based on a genetic profile. While DNA is a significant piece of the puzzle in a criminal case, it still does not, by itself establish the identity of a person beyond a reasonable doubt.

That 0.1% of our genetic profiles that make each of us unique is used to generate a genetic profile. Within that 0.1% profile, DNA analysts will typically use a graph that shows different peaks, which shows the different points where our DNA is most likely to be unique. One of the common issues that arises in DNA evidence cases is that DNA profiles are not clear enough to conclusively identify one particular person. Typically, DNA analysts try to look at 16 different “markers” or points where DNA should be different from one person to the other. Unfortunately, though, DNA is often damaged from exposure to moisture or extreme temperature, meaning that they can only look at a few of those unique markers to generate a partial DNA profile.

The way to think about it is simple: the more markers that an analyst looks at, the more complete the profile, and the more that the analyst can narrow down the list of potential people that have that profile. The fewer markers the analyst is able to identify, the greater the number of potential people having that profile, which in turn means the greater the reasonable doubt. In other words, it really is all about the numbers.

But even then, let’s say that the analyst was able to come up with a full genetic profile of a person. Does that mean that the prosecution has a suspect dead to rights? Likely not. Remember the previous post about how easy it is to transfer DNA? Just because there may be DNA, does not mean that a prosecutor has proven their case beyond a reasonable doubt. Even then, especially in smaller communities like the Mississippi Delta, a full genetic profile does not necessarily point to one particular person, especially if the actual culprit is related to the other person.

The thing to remember is that even though DNA evidence is a powerful tool in criminal cases, it should be considered a piece of a much larger puzzle. When looking at a case where there is DNA evidence, it’s important to take a step back and look at other evidence to place a particular person at the scene of a crime.