If you guessed that they mostly get it wrong, you guessed right.
Let’s hit a few popular myths: DNA and calculations.
DNA takes weeeeeks to get back. 6 weeks would be a good time in today’s standards. Not a few hours. Not even close.
If you’re ever wondering how fast DNA could be obtained, look at celebrity cases. That’s about the fastest they can do it. And it’s still often weeks. There used to be a lab tech with a pipette, measuring and adding chemicals. Now we add it all to reservoirs in a machine that doses reagents and runs the whole thing for us. It takes a good handful of hours still. Things have to sit or shake or rock sometimes and wait. The machines are great–any lab tech who’s spent hours pipetting will agree, but even more than the human labor is the consistency. The likelihood that there’s a calculation error or something is knocked over or mis-dosed is much lower with a machine.
So why can’t they run the DNA in a few hours? First, there’s a backlog. A big one. There are higher and lower priority cases. There are also only certain labs that are qualified to do legal level work. So you might do a home paternity test or want to know if your twins are actually identical, and that could be faster, but it won’t hold up in court. Also, once the process is started, you don’t get to stop it. So just because some bigwig dies amidst scandal does give us enough reason to stop the things that are already running.
There’s also the issue of chain of command. This is not like where you pluck a hair and grab a toothbrush and send it in the mail. There may also be issues of obtaining the DNA. The evidence might have to go to multiple labs (all with chain of command) to get blood out of a shirt and then get it tested and after that get it analyzed! More than one person’s blood in a sample? That’s additional testing. So, that’s going to take a while. ✅
Another thing–and this one is truly scary–is that most people don’t understand how the calculations used for DNA matches work. And sometimes the labs don’t either. The DC crime lab hasn’t been accredited for some time. They lost their accreditation for miscalculations. OUCH 🩻🩻🩻
For starters, we aren’t analyzing the whole genome. Your entire DNA code is NOT getting fed into the system. ❌❌❌ So a match isn’t a match to YOU, it’s a probability.
We only test areas with high variability. Like eye color, hair color… genes we know will be radically different in a lot of different people. Testing for functioning liver enzymes? Not useful. 99+% of people have that. It doesn’t tell us someone does or doesn’t match. Same with the gene that makes sure you have eyeballs, or lungs. Initially we were testing 8 loci (areas of high genetic variability) now CODIS demands 16, but many places test 27 up to 45 points of match. Which you may have already guessed is much better.
It’s easy to multiply numbers we know–but while the math can be right the matching isn’t. DNA doesn’t travel independently. Think of it like this: If 10% of the population has red hair, and 10% of the population has green eyes, then 10% x 10% = 1% Easy Peasy. and also WRONG. 😬😬😬
Red hair and green eyes are linked. In fact, both the first numbers can be correct (10% and 10%) without the calculation working. About 8-9% would have red hair and green eyes, because the genes commonly travel together. This is fine and no one cares, until the lab says only 1 in 400 million people have the DNA left at the crime scene. And they aren’t right. One news channel did a story on a lab report of blood at a crime scene being a 1 in a million match, but everyone on the program tested their blood and FOUR PEOPLE matched the profile. 🧬🧬🧬
So, no, your movies and TV aren’t getting it right. It makes for quick, 1 hour storytelling, but the real world is going to be more difficult to tell. I’ll come back in a future blog and tell you how good we have it, too!
If you’re here, you’re probably a reader. So how about some good book series with forensics in them:
The Kay Scarpetta series: If you haven’t read these yet, you should. Patricial Cornwell did a lot of research at the Body Farm at the University of Tennessee (my home school for forensics!) She also wrote a short non-fiction piece about Jack the Ripper and how we finally ID’d him! You can get Chasing the Ripper on Amazon.
The Body Farm series by Jefferson Bass. From the man who did forensics himself Dr. Bill Bass. Jefferson Bass is a writing duo of Dr. Bill Bass who founded and ran the UT Body Farm for decades and Jon Jefferson an award winning journalist and thriller author. These are the real deal! They also have a short, non-fiction book on a famous forensic case. *And don’t ask me because it’s just such a small world but I was one of Dr. Bass’s last students at UT (He was a guest professor in our program) and also I know Jon Jefferson personally from when I was a kid! Crazy.
And if you haven’t started it yet, you should be reading my NightShade Forensic FBI Files. Like Dr Bass, I have degrees in this stuff, and like the others, I LOVE to write and tell stories! I promise, I got it as right as I could.
