One of the biggest misconceptions about police investigations is the idea that DNA evidence is both easy to find and is easy to use. Every television show on the topic has DNA evidence at every scene, and after maybe a day or two, the forensics squad finishes analyzing it and finds who was present at the scene of the crime. However, that isn’t how it works in the actual world.
First of all, it takes more than a few seconds of swabbing to even find DNA evidence that would be passable in court. There can be DNA from anyone who has been near the crime scene tainting any evidence, including police that aren’t careful enough. DNA comes from anywhere, and isn’t always good to analyze. Also, with every cop show on TV using DNA evidence in every episode, criminals are taking more care in modern times to not leave any (a side effect of the genre.)
In addition, it takes more than a few days to process samples. It normally takes a couple of months to finish the DNA testing, can take up to a year and sometimes cases are even resolved before the DNA evidence comes in. I can’t even hope to explain the science behind the testing, but suffice to say it is very complicated, its not as simple as plugging the sample into a computer that will analyze it overnight.
The problem with the public misconception surrounding DNA evidence is that both the public and jurors are biased in their expectancy of DNA evidence. Since it is extremely hard to analyze, when mistakes are made (and they are made,) it is a lot harder to refute. It also makes people more inclined to be cooperative with police with the hopes that DNA evidence will prove them innocent, but in reality the free talking with police only helps to incriminate them more, especially if/when DNA evidence isn’t found, or rarer, there is a mistake and it makes them seem guilty.