Idaho murders: Suspect was identified through DNA using genealogy databases

YES there is.

PCR can make things up when it goes wrong, which can be as easy as getting the acidity wrong (acidity will cut DNA, which will then recombine into new sequences randomly, so will UV light. Both of these factors, you can bet your firstborn, were present in the sample). PCR (the kind used for sequencing, not the kind used for identification of viruses) does not fail when it is not given DNA or when it's given somehow bad DNA, as everyone in a microbiology lab has probably experienced, it just makes things up. If there is any DNA in the sample to trigger PCR to start, it will "finish". Just ... potentially with a lot of made up endings.

Given what exactly DNA is, and how this was collected, the odds of errors external to the testing procedure itself is pretty damn high (tiny sample, contaminated by loads of frankly incompetent people (police, whatever else you think of them, can seriously improve handling of samples. I'm not even arguing foul play here), contaminated/partially eaten by bacteria, irradiated by UV (which first mutates, then destroys DNA faster than you can say skin cancer), then this was inserted into a database with millions of samples.

Oh, and labs have a financial incentive to make this evidence stick.

Then the output: sequences are a LOT of high probability guesses (millions). So you will never have a 100% match between a sequence, as in a string, and a sequence you found. The output of gene sequencing is not the full genome, but a large amount of short sequences that don't quite fit, but almost, where an algorithm then extracts what might be called "globbing pattern" (if DNA is AGCCAGCAATA, the match might be AG?CA*AAGA (note the mistake at the end T->G). Yes, this is exaggerated, and yes, there's no '*', there's a special marker for "up to X letters missing here", where X can vary).

Important: these patterns contain mistakes. There are ZERO actual DNA sequences that match the output of sequencing. That's where probability comes in.

You do not get the actual sequence (although a "highest probability" match without ? and * can be produced, with the very important caveat that it's a guess with not all that high a probability. That's why they probably matched by matching the "globbing patterns" from samples in the database vs the evidence and then selecting the highest number of matches, rather than comparing an actual DNA "string").

One very relevant question to ask is "what was the probability of this match and what was the probability of the second best match?" (because it's going to be something like ~85% for best match and 75 or more for second best match, and there will be 100+ 20% matches)

And then there's the statistics problem. The police will focus on the odds that THIS match, BY ITSELF, happened. But this is not one match! This is the outcome of millions of matches! The vast majority were negative matches, and then a few hundred/thousand partial matches. That's how the misdirection works. The correct question to ask is "what are the odds, given a true negative rate, of a match if there shouldn't be a match?".

Why? Let's calculate: true negative rate 99.999%, a million people in the database. Odds of a false positive? 1-(99.999% ^ 1000000).

The odds of them fingering a random suspect when there is no positive match is thus: 99.99546023401903%.

As you can see, the more people in the DNA database, the less you can trust the results. Of course, you cannot, honestly, sidestep this problem by checking 10 databases.

This DNA match can be a starting point for an investigation. It is not valid evidence, despite the reputation DNA has. But you can bet anything the prosecutor will attempt to use DNA evidence as the word of God in a trial.

And where there is no question about at all, is that the police used people's DNA (not the murderer's) for something those people have never given permission for.

Pretty sure this is sarcasm, but for general interest I'll mention the Phantom of Heilbronn (https://en.wikipedia.org/wiki/Phantom_of_Heilbronn), "responsible" for multiple murders, but really just an employee at the company that made the cotton swabs that got used for DNA collection.

Do all 7 people have a motive and no alibi? Probably not.

It's been done exactly that way before.

https://www.kold.com/2022/09/29/dna-genealogy-led-arrest-pho...

Which paper? The one pointing out that links are easy to determine with only a small genetics database? Why would I care about that, I want law enforcement to have (audited) access to 100% of the populations genetic records, so I'm not concerned about how small a sample is needed.

A foreign adversary hacks the ancestry database and creates individually targeted genetic attacks.

Sure they can make evidence up, but the logic is that even authoritarian regimes need an inner circle of honest supporters. Think CCP or USSR, they do honestly believe in what they do was right.

What I'm more worried about is insurance companies using this info to say you are part of a cohort expressing allele group X% and is thus more likely to Y, and then acting accordingly based on that info. What if in the future your grandchild gets told they express an allele that gives them a propensity to alcoholism, and on those grounds is barred from entering certain establishments without losing coverage, or without permission? It sounds outlandish, but it's not when you consider in some of our lives, we were born able to buy alcohol at any age, then 16, then 18, then 21. Recently in the past 5 years I've heard more than one conversation about possibly revisiting this to include smoking at age 21, and limiting the size of sugar drinks in a single purchase.

I don't consume sugar or alcohol, but it's also not my choice to say what you should do, especially not because of your genetics, yet if I were an insurance company we sign a contract that gives me that right, so why enable it?