Many believe that if there is DNA at the scene of a crime that matches a particular suspect, then that means that it is an open and shut case. Nothing could be further from the truth. While, traditionally, DNA evidence has been used to resolve criminal cases, it is far from foolproof.
DNA is easily transferable. Anyone person can shed thousands of skin cells every hour. In the real world, this means that there is a several person’s DNA at any one particular crime scene, and the longer a person was there, the more likely the person’s DNA remains there. In other words, at any crime scene, while law enforcement could be looking at one particular suspect, the reality is that DNA evidence, if collected properly, could lead to dozens of suspects, if not more.
This also leads to another concept about DNA: it travels. Here is an example. Person A shakes Person B’s hand. Person B’s hand has now collected Person A’s skins cells, just as Person A has inadvertently collected Person B’s skin cells. Person B then goes and touches a cash register at a local store. Not too long after that, the store is robbed by Person C, who has a similar build and appearance to Person A, and touched the register without wearing gloves. Law enforcement works the scene, and even though they could not lift any fingerprints, they did collect some skin cells. After doing DNA analysis, law enforcement determines that there are three possible suspects, including Person A, who never set foot in the store.
We’ll explore some more flaws about DNA evidence in future posts, but the thing to remember is that DNA, like everything else, is not foolproof. Prosecutors tend to rely too heavily on DNA evidence to gain convictions, but the harsh reality is that they should never rely just on DNA to prove their case.