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Imagine a case that's been cold for decades. No leads, no suspects, families left without answers.
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And then suddenly, one tiny bit of DNA changes everything. Thanks to cutting-edge science, we're seeing more
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breakthroughs in cases than ever before. And it's mostly because of DNA. So now,
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I'm breaking down five powerful types of DNA testing that investigators use to solve crimes and sharing the real cases
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where [music] those tests uncovered the truth. Starting off with number five. Investigative genetic genealogy, [music]
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or IGG. You probably heard a lot about IGG in recent years. But what is it exactly? Investigative
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genetic genealogy brings forensic DNA analysis together with traditional genealogy to develop leads in criminal
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investigations or to identify unidentified human remains. Investigative genetic genealogists or
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members of law enforcement can upload DNA profiles from a crime scene or from remains to certain genetic genealogy
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databases. And from there, they work on identifying genetic relatives of the person whose DNA they have and build out
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a family tree with that data. After the family tree has been built out, police potentially look to obtain a DNA sample
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from someone in that family tree to compare against the original sample. One notable case that has been solved in
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part thanks to IGG is the murder of April Marie Tinsley. April was just 8 years old when she was kidnapped,
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sexually assaulted, and murdered in the spring of 1988. Biological evidence was collected at the
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scene, but sampling and testing protocols weren't advanced enough yet to solve the case. But by the early 2000s,
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investigators were finally able to pull a DNA profile from the sample and upload
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it to CODIS. But no matches [music] were immediately found. That meant that it was likely that the perpetrator's DNA
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had never been uploaded to the CODIS database in connection to any other crimes.
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So the case sat cold until 2018, >> [music] >> when investigators retested the sample
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that they had to get a profile suitable for GEDmatch, which is a public opt-in DNA database. Seriously, anyone,
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including you, can upload DNA to GEDmatch. From there, genealogist CeCe Moore used family tree mapping to
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identify John D. Miller, who had lived not too far from April at the time of her murder. Investigators knew Miller
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probably wouldn't turn over his DNA sample for direct comparison willingly. So they collected his abandoned DNA by
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obtaining used condoms from his trash. Then, when they did a direct comparison to the sample they had in April's case,
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they found out it was indeed their guy. In 2018, John Miller pled guilty to murder and child molestation in
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connection with April's killing. He was sentenced to 80 years in prison. So though it took some time and
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technological advances, DNA led to justice for April. Number four. Familial searching. What if solving a
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case didn't come down to the killer's DNA, but their relatives? That's the idea behind familial searching. Instead
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of looking for a perfect match in CODIS, the US national DNA database, investigators look for partial matches.
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[music] DNA that might belong to a parent or sibling or child of the suspect. Now,
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CODIS and how it works is a beast all on its own. So if that's something that you
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want to dive deeper into in a separate video, be sure to like this one. Let me know what about CODIS you want to learn
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more about in the comments below. [music] I'm doing a deep dive. But familial searching helps
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investigators identify potential relatives of people whose DNA was collected from a crime scene.
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It doesn't necessarily lead investigators straight to their suspect, but it may help them find a close
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relative of their suspect. [music] And in order to get that sort of hit, that relative's DNA has to have already
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existed in the DNA database, whether that's [music] by choice or because they have committed a crime. Now, there are
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laws around this type of testing in some states because of privacy concerns. A state that approves the use of
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familial searching to find suspects is New York, where the murder of Wendy Jerome occurred in 1984. Multiple
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samples in varying degrees of degradation had been found at the scene of Wendy's murder. And they were all
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tested multiple times in multiple ways. Until finally, in 2020, a test of one of
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the samples led to a familial hit in CODIS. >> [music] >> That hit was for a relative of Timothy
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Williams, the man we now know was responsible for Wendy's killing. His conviction made history because it was
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the first case in New York state to be solved using familial DNA testing. Number three. Mitochondrial DNA, or
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mtDNA analysis. How do you catch a killer when the only evidence left behind is a single strand of hair
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without a root? That's where mitochondrial DNA, or mtDNA analysis, comes in. This type of DNA is pulled, as
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the name suggests, from mitochondria, and it's always passed down from mother to child. Many people share the same
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mtDNA, so it cannot be used to identify unique individuals. But it can link someone to a maternal line. And because
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it works even when DNA is too degraded for other tests, it can give investigators a critical lead when other
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methods can't. That's exactly what happened in the search for the Gilgo Beach killer. Investigators found
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degraded, rootless hairs on the burlap sacks used to wrap some of the victims up in this case.
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And by 2023, a lab was able to successfully pull an mtDNA sequence from the hairs.
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Now, there are several ways to do this, and we don't know exactly what method they used because they've not made that
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public yet. Probably because this case is still going to trial, maybe. But they extracted DNA from those hairs and used
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whole genome sequencing to develop a profile. Then they used that sequence to narrow down a pool of possible families,
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including the family of Long Island man Rex Heuermann. This mtDNA sequence was then compared against a reference sample
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that had been obtained from a pizza crust that officials say Rex Heuermann had thrown away, which is another
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example of voluntarily abandoned DNA. That allowed them to get a warrant, collect a buccal swab, and then
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establish a direct match. Heuermann was charged with murder in the deaths of at least seven women spanning
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three decades. One thing I do want to note about mtDNA evidence is that it is rarely the only evidence used to
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prosecute someone. It doesn't prove identity by itself, remember, but it can be the crucial piece that backs up other
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evidence and helps prosecutors close in on a suspect. Number two. Y-STR DNA. Now, this type of testing zeros in on
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one thing and one thing only, the Y chromosome, which only exists in men. So it can only trace DNA passed down from
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father to son. This type of testing can be particularly powerful when evidence has a mix of male and female DNA, like
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for example, what could be present in a sexual assault kit. By isolating the Y chromosome, labs can
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pull out just the male DNA from the sample. >> [music] >> One chilling example of this? The 1991
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yogurt shop murders in Austin, Texas. [music] At the time, Y-STR testing was brand
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new. And the district attorney overseeing the case decided to give it a shot. Investigators believed that at
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least one of the victims in this case had been sexually assaulted. And this test paid off. They pulled a partial
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male DNA profile from the evidence. >> [music] >> But in the '90s, that profile didn't
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match anyone in the system, so the case went cold. Decades later, in 2025, everything changed when police received
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a report from a South Carolina state lab that linked the yogurt shop unknown Y-STR profile to a known Y-STR profile
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from a 1990 sexual assault and murder out of Greenville. The suspected killer? Robert Eugene Brashers, a known serial
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rapist and killer who had taken his own life back in 1999. From there, investigators were able to
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use other evidence to connect Brashers to the yogurt shop murders, bringing long-awaited answers to a case that
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haunted Texas and us crime junkies for more than 30 years. Number one. Short tandem repeat, or STR analysis.
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When it comes to solving crimes with DNA, this is the gold standard. STR analysis, short tandem repeat testing,
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[music] compares short, repeating DNA sequences between a DNA sample giver and DNA evidence collected from a crime
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scene. It's powerful because it gives investigators a yes or no answer. Either it is a match or it's not.
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STR analysis can be used to identify men or women, as it examines DNA patterns found within the human genome. It is the
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only type of DNA analysis that can be used to convict someone in court because it's a one-to-one comparison. [music]
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And because STR analysis either finds a direct match or no match at all, it can also be used to exclude individuals from
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a suspect list. And one of the most infamous cases cracked by STR? The hunt for the Green River Killer.
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Some detectives originally working the case, even back in the day, recognized the potential power of DNA. And so they
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held on to DNA evidence even though they couldn't do anything with it in that moment. But they figured that could
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change as technology continued to advance. And sure enough, in the case of the Green River Killer, that paid off.
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Gary Ridgway first came onto police's radar in 1983. And in 1987, they eventually had enough evidence to search
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his home in connection to their investigation. And during that time, police took samples of Ridgway's hair
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and saliva. Again, even though DNA testing was still in its infancy. Fast forward to 2001, technology had
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advanced and investigators finally had what they needed and they were able to directly compare Ridgway's DNA to a
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sample pulled from a Green River victim via STR analysis. The original STR analysis was compared to sperm found on
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three victims: Cynthia Cookie Gene Hines and Marcia Faye Chapman, [music] discovered on August 15th, 1982. And
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then Carol Anne Christensen, found May 8th, 1983. After nearly two decades of unanswered questions, the Green River
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Killer was brought to justice. Ridgway was convicted and sentenced to life in prison.
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These are just some of the cases where though it may have been delayed, justice was served through the help of DNA
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testing. If you want to go deeper into any of these, you can find the full stories on Crime [music] Junkie wherever
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