True crime shows love to talk about DNA solving cold cases. They make it sound like magic – a drop of DNA goes into a machine, and out pops a criminal’s name.
But as an investigative genetic genealogist, I can tell you the reality is way more fascinating.
The Game Has Changed
Ten years ago, finding DNA at a crime scene meant one thing: you needed a suspect’s DNA to match it to.
No match? Case goes cold.
Today, everything’s different.
That same DNA can now lead us straight to a suspect through their family members – even distant cousins they’ve never met.
And it’s working. Every single day, cases that went cold decades ago are getting solved.
Let me show you exactly how.
It’s Beautifully Simple
Most people think we need immediate family to solve a case – a parent, sibling, or child.
Not even close.
The reality? We solve cases using DNA from second, third, or even fourth cousins.
People the suspect has never met. People who don’t even know the suspect exists.
Every day, more people take DNA tests. Every day, more connections appear. And any one of these tests could break open a case that’s been cold for decades.
Multiple distant cousins lead us to shared ancestors. Those ancestors lead us to our suspect.
This isn’t about lucky breaks. It’s systematic. Scientific. Replicable.
The same process that caught the Golden State Killer is solving cases in every state, right now.
And it’s working. Every single day.
The power of this technique grows with every DNA test. Every new test tightens the net. Fills in gaps. Creates new connections we can use to solve cases.
The process isn’t nearly as complicated as you might think.
It’s actually beautifully simple.
Breaking Down the Process
It starts with crime scene DNA. First step? Run it through the FBI’s database.
But when there’s no match there, the genealogy work begins.
We upload that DNA to GEDmatch and FamilyTreeDNA – public databases where users have chosen to opt in to help law enforcement solve crimes.
Not Ancestry. Not 23andMe. Not MyHeritage. These are completely separate platforms.
Then we start building family trees from the matches we find. It’s precise. Methodical. And it works.
Building Trees and Finding Connections
When we first look at the DNA matches, we might see several distant cousins. Maybe a second cousin here (if we’re lucky), a third cousin there.
Each one of these matches is like a signpost pointing toward our unknown person.
We don’t need close relatives to solve a case.
A couple of second, third or fourth cousins sharing DNA with our unknown person? That’s enough to solve the case.
We look at how these matches connect to each other, and how they might connect to our suspect.
The Detective Work
We start building family trees backward in time, looking for common ancestors between our DNA matches. Sometimes we’re going back 4-5-6-7 generations to find where these families connect.
When we find those common ancestors, we know our unknown person must descend from them as well.
Suddenly, instead of looking for a needle in a haystack, we’re looking in a specific section of a specific haystack.
We use every public record set at our disposal:
- Old newspapers
- Census records
- Vital records
- Obituaries
- Yearbooks
- Social media
- etc
Narrowing Down the Suspects
As we build these family trees forward in time, we’re looking for every single person who could possibly be our unknown person. We consider:
- Age when the crime occurred
- Location around that time
- Gender
- Ancestry background
Sometimes this gives us a single perfect candidate. More often, we end up with a small group of possibilities.
That’s when we hand everything over to law enforcement.
The Final Steps
Here’s something crucial that most people don’t understand: no one gets arrested based solely on genetic genealogy.
When we identify potential suspects, law enforcement still needs to investigate them using traditional methods.
They need to collect their own DNA sample and confirm it matches the crime scene DNA through official channels.
DNA samples of potential suspects are uploaded to the FBI software, CODIS, to see if it matches the crime scene DNA.
We’re not solving cases alone – we’re giving investigators highly targeted leads that they need to followup on.
No more, no less.
The Privacy Question
Whenever I explain this process, people immediately ask about privacy.
They want to know if taking a DNA test means law enforcement can access their genetic information.
Here’s the truth: commercial DNA companies like Ancestry and 23andMe are completely off-limits to law enforcement.
They can’t access your DNA there. Period. End of story.
The databases we use for solving crimes are entirely separate and voluntary. People choose to upload their DNA and opt in to law enforcement matching.
They’re actively deciding to help solve crimes. I encourage you to do the same.
You’re not giving up privacy. You’re not sharing your DNA with police. You’re simply allowing your genetic connections to be visible if they match with a crime scene sample.
The Future of Crime Solving
Every single day, somewhere in America, a cold case could be solved using these exact methods.
Cases that have stumped investigators for decades are being cracked open. Families who thought they’d never get answers are finally finding closure.
And we’re just getting started.
The more people who choose to participate, the more powerful this tool becomes. Every person who takes a DNA test and opts into law enforcement matching makes it more likely that we’ll solve another cold case.
Think about that for a second: your decision to take a DNA test today could help solve a decades-old murder tomorrow.
You don’t have to do anything special (other than opt in). You don’t have to give up your privacy.
You just have to choose to be part of the solution.
Because behind every cold case is a family still waiting for answers.
Author’s note: Obviously I’ve simplified a lot of the technical details in this post. Want to dive deeper? Check out my full guide here.
