How DNA Analysis Led Police to the Golden State Killer

How DNA Analysis Led Police to the Golden State Killer

[INTRO ♪] Back in the ‘70s and ‘80s, a man known
as the ‘Golden State killer’ terrorized California, committing a string of more than 100 burglaries,
45 rapes, and a dozen murders. Definitely a bad dude. Even though the police had DNA evidence from
crime scenes, it never matched any DNA records on file,
so the case went cold … Until last week. By this point, you’ve probably heard about
this man’s capture. But you might not realize that the science
used to crack the case is totally different from standard DNA forensics. So by understanding how DNA analysis is typically
done for crime scenes, we can dive into why the Golden State killer
case is so special. Usually, forensic scientists process DNA with
a method called short tandem repeat, or STR, analysis. The basic idea is that little stretches of
short repeated sequences, like TAGA, are scattered throughout your genome, in specific places on specific chromosomes. Because the number of repeats at each location
tends to vary from person to person, counting them can be useful. Like, they can help match the semen in a rape
kit to a suspect. For instance, you might have 6 TAGA repeats
on a chromosome that you got from one parent, and 10 repeats
from your other parent, while I might have 12 and 15. Now, if the number of repeats at one spot
in someone’s DNA happens to match evidence from a crime scene, that doesn’t necessarily mean much. But if you look at a bunch of repeats and
they all match, you might be onto something. In the US, forensic scientists have traditionally
tested for repeats at 13 different spots in the genome, although
recently they upped it to 20. That’s what’s happening when you hear
about hits in CODIS, the FBI’s database of DNA records. A match is all about probability, and there
are a lot of factors to consider, like how common certain STRs are in a given
population. But if your suspect’s DNA repeats in the
same 13 ways as a sample from the crime scene, the odds that the suspect isn’t the source
are typically about one in a billion. In other words, combined with other evidence, you can be pretty confident that you’ve
got the right person. Of course, DNA analysis isn’t perfect. Contamination is a concern, and there’s
room for doubt in cases where there’s a small amount of
DNA, or the DNA is degraded. These days, standard STR analysis uses a process
called PCR to amplify the DNA sections the police are
interested in. But that can lead to errors, and they might
not get solid data for all 20 repeat locations. Another challenge is that many samples include
DNA from multiple people, like both a victim and the criminal, making
the analysis more complicated. And any positive match still needs to be interpreted. After all, an innocent person might have scraped
their finger and left a few drops of blood behind at a
future crime scene. So that’s how standard forensic DNA testing
works. And if it’s all done right, it can be really
persuasive, as you probably know from shows like CSI. But with the Golden State killer, the cold
case heated up because of a different approach to DNA— one that’s a lot closer to spitting in a
tube to find out your ancestry. Detectives had some DNA evidence that was
collected from a double murder in 1980 and frozen, so
it was especially well-preserved. We don’t know the specifics of what they
did next, but they eventually uploaded data from that
sample onto an open-source genealogy website called
GEDmatch. While GEDmatch isn’t a power player in the
commercial DNA industry like 23andMe or, it runs on the
same kind of information. So someone might use one of those services
to get raw genome data, then submit it to GEDmatch to help find long-lost
relatives and piece together their family trees. The FBI created the DNA profile of the Golden
State killer in their own labs, from that well-preserved sample. And they probably generated the same kind
of data, by looking for single nucleotide polymorphisms,
or SNPs. These are individual As, Ts, Gs, and Cs throughout
the genome that we know vary between people and can be
passed down from parents to kids—and because of that,
they’re useful biological markers. In a way, SNP analysis is similar to STR analysis, except it’s cheap and easy to test for tens
of thousands of these puppies at once. So that’s what’s going on when you mail
in your DNA. Most companies aren’t directly sequencing
your entire genome. Instead, they’re using technology that checks
your DNA for a whole bunch of SNPs. Most importantly for detectives, because there
are so many SNPs, and they change less over time from mutation, SNP testing is much better than STR analysis when it comes to identifying far-flung relatives. So, once the detectives on the Golden State
killer case uploaded the genetic profile of their suspect, they looked for similarities among GEDmatch’s
900,000 other profiles. Their killer hadn’t uploaded his own data,
but some of his distant relatives— like, third and fourth cousins—had. These are people who would share about 2%
of their DNA with him at most. But it was enough of a lead to build potential
family trees—some 25 in all. Within 4 months of getting some initial hits
on the genealogy site, police officers had painstakingly narrowed
their focus from thousands of relatives to one man. He was the right age, and had lived in California
during the crime spree. To confirm that he was the Golden State killer, they needed some of his DNA to test for a
match. So they put him under surveillance and grabbed
his trash. They used something with some of his cells
on it: maybe a straw, soda can, or used Kleenex—we
don’t know what exactly. And then they did a DNA test, probably STR
analysis, and got a match. Just to be sure, they checked again. Another garbage item, another test—and another
match. After 44 years, they had identified
the Golden State killer. He was a former cop named Joseph James DeAngelo, now age 72, living in a suburb of Sacramento, California. Now, this case isn’t the only time DNA has
been used like this, but it’s one of the highest profile cases. And it’s likely to have people talking for
a while, especially about data privacy issues. We won’t get into that here, but it’s
definitely something people are thinking more about, as investigators
realize how many ways they might be able to use DNA. Even if it involves way more work than TV
crime dramas ever show. Thanks for watching this episode of SciShow News! If you want to learn more about forensics, you can check out our episode that dives into
a lot more crime scene science. And if you just want to keep thinking about
the world more complexly with us, you can go to youtube/scishow and subscribe. [OUTRO ♪]


  1. This same technique was used last month in the identification of Marcia King, who was murder 37 years ago and was well known among internet sleuths as the Buckskin Girl.

  2. I feel this is just the same as posting anything online. users should know just like posting to Facebook, YouTube, etc anything you post publicly can be used against you or others. So long as the police don’t skip that last step of testing the suspect’s dna directly, I don’t see anything wrong with what happened or is happening.

  3. 😏The age of Serial Killers might be "dying" due to better technology and science.
    Heck if I had a relative that could be a serial killer I would NOT mind giving my DNA to help catch them!

  4. I have an interesting idea! It could be possible to map the genome and it's function I'm animals by tracking the number of changes in the genome and any physical changes.

  5. Why don’t you make a video on the alternative theories about the Universe on YouTube this would be interesting and good for the YouTube community!!!

  6. Can't forget the possibility of human error in interpretation and underlying biases. There are some truly sad findings in the literature on the misuse of DNA evidence because it is so compelling

  7. Great video, I’ve never heard DNA testing explained so clearly before – helped my basic understanding!

  8. IMO, all public servants (police, judges, politicians, and the like) should have their DNA recorded… Especially police officers!!!

  9. I read a lot about this guy a while back and there was one thing that always stuck out to me. A lot of victims reported that he had a very disntinct smell. Not as if he hadn't showered in a month – something else. Something sickly. Has anyone ever managed to find out what that was?

  10. When discussing the FBI we should also consider their ability to plant DNA at a crime scene and fake evidence.

  11. Of course the murderer was a cop. Duhhh. When you know the law doesn’t apply to you, this is what people do.

  12. Forgive my ignorance, but is it legal for the police to swipe your trash without your knowledge in an attempt to collect incriminating evidence?

  13. But can't you just find a strand of hair and voila you have your suspect, or enhance a photo so much you see the reflection in a water drop of the murderer. #CSI logic

  14. Cops at the time didn't seem committed to catching the killer. They think the killer is a cop, but don't obtain fingerprints and DNA from cops to rule them out. The crimes start and stop depending on the location of one cop. That same cop is fired for stealing dog repellent and rope. DNA was not needed to solve this crime, just more observant cops.

  15. I mean I'm happy that they caught that killer but c'mon people!
    It's bad enough people share their whole life on social media now they share their DNA at this level?! It's sad.

  16. in short :
    – DNA isn't enough as contamination is a huge issue.
    – Corruption and abuse by police officers is a huge issue.
    – Companies like 23 and Me selling private data is a huge issue.

  17. A lot of people seem to be concerned that the police can cross-reference DNA across a database like this, but… it's a public database. You could do it too, if you had the tech. And even if it wasn't public, if you get a 23andMe test, congrats. You've sold a copy of your genetic profile to a company, and now they can do whatever they want with it. As well as a link to all of your other relatives, forever. Until they create a law that says otherwise, you've essentially "first sale doctrine"'d yourself.

  18. Now science just needs figure out how to stop or reverse aging. So that the golden state killer could serve his time, since he already lived a long life and is about to expire himself.

  19. I learned everything from the CSI dramas on TV.

    I know that the real world doesn't work that way, but I would rather be over-prepared than under-prepared.

  20. If there's a 1 in a billion chance of a false match, doesn't that mean that if we had a database of everyone's DNA that we would get 6-7 false positives on average for every DNA test? This seems way too high to do anything other than eliminate suspects to me.

  21. Really thought DNA was going to slowly disappear from courts because it can be manufactured now, can essentially make it look like anyone has done anything… (not saying that is what has been done with this case!)

  22. There was an Australian called Ned Kelly….

    As I need to leave in 120 seconds I will just give the short version:
    This technology targets a suspects family till the police use other tests to narrow it down.
    How long till they have several 'possible suspects' because they can not narrow it down and simply harass the whole family as 'bad apples?'

  23. Going through the comments here is a ride. It is not a violation of privacy to use DNA voluntarily submitted to a public database to construct a profile. And it isn’t as though just by virtue of being a relation the guy was convicted. There were still thousands of possible suspects that had to be narrowed down, and the forensic team still cross referenced their primary suspect’s actual DNA to confirm a match. And now he will go through traditional criminal proceedings. There’s nothing about this process that strikes me as illegal or a “slippery slope”. I think this is a fantastic use of new technology that will hopefully put more criminals away and de-incentivize crime.

  24. Future criminals take note. Don't upload your DNA to GED and stop all your relatives from uploading theirs. Good luck with the latter though.

  25. I don't really object to this, but it does raise an interesting ethical issue regarding the 'ownership' of genetic information. You, as an individual, can't entirely stop authorities, insurers or the public at large knowing about your DNA because you can't control the actions of those related to you. When people make DNA data publicly known, it isn't only their data. Most legislation on privacy, to my knowledge, doesn't really take that into account because it's geared (understandably) towards the rights of the individual.

  26. Confusing when mixing 13 and 20 STRs (@2:13), especially when saying them as "used today".

    Also whats up the mentions of an episode (vaguely hinted in this one) being a complexly production ?

  27. The Ancestry DNA kits have gone down in price by about 50% recently. Hopefully people will wise up now so Ancestry and the others won't be able to give them away.

  28. So a US agency got data from 23andme or ? If that's true, that is a serious security breach. You tiptoe around where the police got the data from – but I doubt "thousands of relatives" were in a criminal database.

    And you talk about it like it was the most normal thing. The US gov has access to the DNA of its population – great, 1 suspect caught. /s Benjamin Franklin is turning in his grave. Sad and disgusting.

    Shame on you SciShow – not for picking a side – but state the facts, say where the data came from.

  29. Interesting video, if people are interested in other methods that are used. There's a video from James Corbett that goes over other types of methods that forensic scientist use and gives reason to doubt some types of forensic analysis. -peace

  30. I read the title as "Golden Skate Killer" and immediately thought I was about to hear that Paranoia Agent was based off of true events.

  31. When are y’all gonna learn to burn/submerge/dissolve your evidence/victims? THIS ISN’T ROCKET SCIENCE, PEOPLE!

  32. Serial killers can be very smart Edward Kemper had a iq over 140+ if hadnot turn himself in no telling how many people he could of killed very scary heis so smart he himself knows he should've never be let out of prison

  33. FYI. The site name doesn't spell out the first 3 letters. It's referred to as GEDmatch (one word with a J sounding G). GED refers to file type known as a GEDcom (also said as one word with a J sounding G). That is the file type used for family trees. The sites original purpose was for comparing family trees.

  34. Not DeAngelo ! he never made the calls. miss managed D.N.A and only a few matchs in code he is not a true match to murderer !!!

  35. the reason police want to take his D.N.A an picture him!!! these are true FACTS . never made the phone call's either . these are proof police lied !!!

  36. Interesting I was watching a show about this criminal a month ago and of course they hadn't caught him at the time of this documentary. ..

  37. Here's an idea: Uploading DNA from unidentified bodies to ancestry websites in hopes of finally identifying them!

  38. I wonder how long it will take for some defence lawyer to wake and smell the coffee? The "experts " keep quoting the same line " the chances of a match are 1 in ( insert improbable figure)"  Since the incidence of identical twin births is about 1 in 200 of live births, the chances of an IDENTICAL DNA sequence has to be the same 1 in 200.  There is also the question of how many of the large number they quote in their identical match speech would result in a live and how many a dead ( genetic problems killing the foetus) birth. It seems to me that the " experts" are deliberately misleading the courts and the people.  I do not deny the usefulness or the accuracy of DNA matching or the fact its usually pretty conclusive for either the prosecution or in some cases the defence. I just wish they would stop trying to "over egg" the pudding.

  39. Data privacy? Sorry but if peoples lives are at stake, we should do anything we can to help. And if that involves giving a DNA sample or info, i'm in.

  40. Ever since youtube, we no longer have tolerable narration and deep voices. We've got Elmo after elmo after flamboyant elmo. Ugh this blows.

  41. Police didn’t catch him it was a Mr Hole investigator. Police only covered up back in 1979 when Auburn Police Chief ignored red flags and MO of the cop he terminated who ended up shining a flashlight in his daughters bedroom after threatening his life. Let him go his merry way to get a cop job in Visalia.

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