Years ago, before DNA came into prominence, many people who committed crimes probably got away with it. This may explain the number of unsolved and cold cases. At the same time, there have been several cold cases that were finally solved after decades because someone was smart enough to collect and preserve evidence that, when tested years later, proved beyond a shadow of doubt that a certain person was the perpetrator.
DNA evidence is compelling and pretty much irrefutable. Today, criminals still make mistakes (thankfully) and aren’t careful about leaving some kind of DNA evidence and so they are apprehended and brought to justice. Let’s take a look at the interesting world of DNA and how it can be found at a crime scene.
1. Body Fluids
A very common source of DNA at a crime scene is body fluid. There are many ways that body fluid can be left behind at a crime scene. Sometimes, a criminal just doesn’t know and it is left by accident, perhaps in a state of panic. Then there are other times where the perpetrator leaves it behind through sheer stupidity. Saliva, sweat, semen, blood and urine all contain DNA. Virtually any secretion or excretion will provide DNA. There have been instances where a person was murdered and the perpetrator left a clearly visible bite mark on the body.
A lot of the time, there may be a knife involved, which means even the criminal could end up accidentally cutting themselves, causing blood to drip. In a rape, semen can be deposited. Even if something has dried up, it can be scraped and collected as evidence.
2. Hair & Skin
A criminal may lose hairs or skin at a crime scene and if he or she has a record, then they will be caught if their info is in the database. The presence of skin and hair can yield enough information if you perform DNA testing. A lot of the time in these major crimes, there will be some kind of a struggle. Hairs may be yanked out and fingernails can trap skin cells if the person tries to defend themselves by scratching at the perpetrator.
Evidence collection must be done meticulously in order to find such samples, even a single hair sometimes, which can say so much. For example, someone can claim that they were 300 miles away when the victim was murdered and even provide an alibi, but if their skin was scratched and these cells were embedded under the victim’s fingernails, that is pretty compelling evidence. The suspect will have a lot of explaining to do!
3. Touch DNA
Touch DNA is useful when there are no other leads and it is the only evidence you have. Every time someone touches something, trace amounts of DNA may be left behind from oils or epithelial cells. Years ago, this kind of evidence was not suitable for DNA profiling but with the advancement in technology, even a little bit of material can now be worked with. The information derived may not be as useful, however, when authorities have absolutely nothing to go on, it could make a difference.
Collecting evidence must be done with the greatest of care. You may have seen in real life (and very likely in TV shows) where evidence collectors are all dressed up from head to toe in special clothing. This is because their own DNA could contaminate evidence. In fact, investigators themselves have to be subjected to DNA tests just in case; this way, if their DNA is found, it can be ruled out.