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How close does a DNA "match" have to be to get somebody tossed in jail? Do they actually require 100%, or is a "match" something less? What's the false-positiv

How close does a DNA "match" have to be to get somebody tossed in jail? Do they actually require 100%, or is a "match" something less? What's the false-positive rate? Would a non-twin sibling's DNA "match"? Yes, I'm aware that, in theory, DNA is unique. As is the theory for finger-prints. But, I'm also aware that theory is rarely reality.

assimpleaspossi 2mo ago
Remember that one still needs proof. My DNA on a victim's clothes does not mean I committed the crime.
- estearum 2mo ago
  In principle. In reality, juries often hold evidence like this (and also-very-unreliable eye witness testimony) in high regard, based on how it's positioned into the narrative.
  - alistairSH 2mo ago
    In reality, juries often hold evidence like this in high regard, based on how it's positioned on CSI:Some-City television.
- alistairSH 2mo ago
  Are you willing to trust 12 random schmoes to make that call correctly? Especially in the face of an overzealous prosecutor?
  - bell-cot 2mo ago
    The fake-it-'till-you-make-it crime lab "scientist" is worse: https://en.wikipedia.org/wiki/Joyce_Gilchrist https://en.wikipedia.org/wiki/Joyce_Gilchrist
  - dpb001 2mo ago
    Exactly. I’ve served on two juries and the experiences left me shaking my head. In one case the judge’s instructions were dismissed by a majority of the jury members with a “yeah, but…”.
  - assimpleaspossi 2mo ago
    The same process we've used for centuries? You got something better? I'm sure you don't. You are also ignoring that the 12 random schmoes are selected by both sides attorneys and given instructions and facts and can still be overruled by a judge (under circumstances) plus the possibility of appeal. Your response is very uninformed at best.
    - alistairSH 2mo ago
      [flagged]
      - deleted 2mo ago
        [deleted]
voidUpdate 2mo ago
According to wikipedia, "the theoretical risk of a coincidental match is 1 in 100 billion (100,000,000,000) although the practical risk is actually 1 in 1,000 because monozygotic twins are 0.2% of the human population", so it looks like some twins will cause an issue for DNA-based convictions, but I think a non-twin sibling is probably diverse enough? I have different eye colour, ears, food intolerances to my brothers, so I feel like our DNA is pretty different ("pretty" on a scale of human to human comparisons, since 99.9% of DNA is identical between humans or something like that). I'd argue that while a DNA match could be a very good starting point for a conviction, other evidence should also be presented, for the reasons you suggest. For example, there is the case of the Phantom of Heillbron (https://en.wikipedia.org/wiki/Phantom_of_Heilbronn https://en.wikipedia.org/wiki/Phantom_of_Heilbronn), where European police found DNA evidence of a woman being at many diverse crime scenes, but it turned out the cotton swabs used for testing were contaminated by at worker at the factory (The swabs weren't certified for police work)
- crote 2mo ago
  That is a coincidental match, though! It's the risk of a false positive when you compare exactly two samples. The problem is that we're proposing a DNA database, so you're now comparing 1 sample found at a crime scene with 300ish million people. That's a 300M in 100B chance, or 1 in 333, of some person having a false positive match. Now combine that with thousands of samples being tested every day (because let's be honest, why wouldn't you use such a database for literally every single crime?) and you're looking at dozens of false-positives per day. It is only a matter of time before it isn't someone with an airtight alibi at the other side of the country, but someone reasonably-close who was just sitting alone on their couch at home all weekend. How are they going to prove they weren't involved in the crime? This is why large-scale DNA matching is a horrible starting point for a conviction. It gives you a false sense of security, and it makes the investigators lazy. In most cases it is far better if DNA is used as the final nail in the coffin when you've already got a solid case against a suspect.
  - actionfromafar 2mo ago
    Sounds like perfect for rich people, they'll have the resources to argue in court.
amiga386 2mo ago
Don't forget the reverse. If your DNA's an insufficient match to your children, they take your kids away. https://womenherald.com/health/the-chimerism-case-how-lydia-fairchilds-unique-genetic-condition-nearly-cost-her-custody-of-her-children/ https://womenherald.com/health/the-chimerism-case-how-lydia-...
- suslik 2mo ago
  This is a really interesting article, even though it seems a little biased towards the mother (which, post hoc, if absolutely fair). Would be very cool to see / read this from the position of the judge as the thing unraveled.
trymas 2mo ago
I think this video can answer your question: https://www.veritasium.com/videos/2021/9/30/your-dna-is-already-in-a-database https://www.veritasium.com/videos/2021/9/30/your-dna-is-alre... I don’t remember the exact details, because I have watched it long time ago, but they don’t need an exact match. Actually it’s more scary - if your distant cousin has DNA “in the system” - you are in it too. This 1M DNAs may “help” match an order of magnitude more people.
- voidUpdate 2mo ago
  I think you're thinking of genetic genealogy, where some of those DNA testing providers (like 23andme) submit their records to law enforcement, and they can see something like "this DNA sample is likely to be a brother of this existing sample", and can narrow down investigations based on that
Izkata 2mo ago
A woman's DNA match to a dead baby from before she was born led to the arrest of her grandmother: https://www.cnn.com/2024/12/12/us/baby-garnet-cold-case-michigan https://www.cnn.com/2024/12/12/us/baby-garnet-cold-case-mich...

assimpleaspossi 2mo ago

Remember that one still needs proof. My DNA on a victim's clothes does not mean I committed the crime.

estearum 2mo ago
In principle. In reality, juries often hold evidence like this (and also-very-unreliable eye witness testimony) in high regard, based on how it's positioned into the narrative.
- alistairSH 2mo ago
  In reality, juries often hold evidence like this in high regard, based on how it's positioned on CSI:Some-City television.
alistairSH 2mo ago
Are you willing to trust 12 random schmoes to make that call correctly? Especially in the face of an overzealous prosecutor?
- bell-cot 2mo ago
  The fake-it-'till-you-make-it crime lab "scientist" is worse: https://en.wikipedia.org/wiki/Joyce_Gilchrist https://en.wikipedia.org/wiki/Joyce_Gilchrist
- dpb001 2mo ago
  Exactly. I’ve served on two juries and the experiences left me shaking my head. In one case the judge’s instructions were dismissed by a majority of the jury members with a “yeah, but…”.
- assimpleaspossi 2mo ago
  The same process we've used for centuries? You got something better? I'm sure you don't. You are also ignoring that the 12 random schmoes are selected by both sides attorneys and given instructions and facts and can still be overruled by a judge (under circumstances) plus the possibility of appeal. Your response is very uninformed at best.
  - alistairSH 2mo ago
    [flagged]
    - deleted 2mo ago
      [deleted]

voidUpdate 2mo ago

According to wikipedia, "the theoretical risk of a coincidental match is 1 in 100 billion (100,000,000,000) although the practical risk is actually 1 in 1,000 because monozygotic twins are 0.2% of the human population", so it looks like some twins will cause an issue for DNA-based convictions, but I think a non-twin sibling is probably diverse enough? I have different eye colour, ears, food intolerances to my brothers, so I feel like our DNA is pretty different ("pretty" on a scale of human to human comparisons, since 99.9% of DNA is identical between humans or something like that). I'd argue that while a DNA match could be a very good starting point for a conviction, other evidence should also be presented, for the reasons you suggest. For example, there is the case of the Phantom of Heillbron (https://en.wikipedia.org/wiki/Phantom_of_Heilbronn https://en.wikipedia.org/wiki/Phantom_of_Heilbronn), where European police found DNA evidence of a woman being at many diverse crime scenes, but it turned out the cotton swabs used for testing were contaminated by at worker at the factory (The swabs weren't certified for police work)

crote 2mo ago
That is a coincidental match, though! It's the risk of a false positive when you compare exactly two samples. The problem is that we're proposing a DNA database, so you're now comparing 1 sample found at a crime scene with 300ish million people. That's a 300M in 100B chance, or 1 in 333, of some person having a false positive match. Now combine that with thousands of samples being tested every day (because let's be honest, why wouldn't you use such a database for literally every single crime?) and you're looking at dozens of false-positives per day. It is only a matter of time before it isn't someone with an airtight alibi at the other side of the country, but someone reasonably-close who was just sitting alone on their couch at home all weekend. How are they going to prove they weren't involved in the crime? This is why large-scale DNA matching is a horrible starting point for a conviction. It gives you a false sense of security, and it makes the investigators lazy. In most cases it is far better if DNA is used as the final nail in the coffin when you've already got a solid case against a suspect.
- actionfromafar 2mo ago
  Sounds like perfect for rich people, they'll have the resources to argue in court.

amiga386 2mo ago

Don't forget the reverse. If your DNA's an insufficient match to your children, they take your kids away. https://womenherald.com/health/the-chimerism-case-how-lydia-fairchilds-unique-genetic-condition-nearly-cost-her-custody-of-her-children/ https://womenherald.com/health/the-chimerism-case-how-lydia-...

suslik 2mo ago
This is a really interesting article, even though it seems a little biased towards the mother (which, post hoc, if absolutely fair). Would be very cool to see / read this from the position of the judge as the thing unraveled.

trymas 2mo ago

I think this video can answer your question: https://www.veritasium.com/videos/2021/9/30/your-dna-is-already-in-a-database https://www.veritasium.com/videos/2021/9/30/your-dna-is-alre... I don’t remember the exact details, because I have watched it long time ago, but they don’t need an exact match. Actually it’s more scary - if your distant cousin has DNA “in the system” - you are in it too. This 1M DNAs may “help” match an order of magnitude more people.

voidUpdate 2mo ago
I think you're thinking of genetic genealogy, where some of those DNA testing providers (like 23andme) submit their records to law enforcement, and they can see something like "this DNA sample is likely to be a brother of this existing sample", and can narrow down investigations based on that

Izkata 2mo ago

A woman's DNA match to a dead baby from before she was born led to the arrest of her grandmother: https://www.cnn.com/2024/12/12/us/baby-garnet-cold-case-michigan https://www.cnn.com/2024/12/12/us/baby-garnet-cold-case-mich...