[mcherm]

> Has this not been done?

No, this has not been done.

> If not, why?

Because it would fail.

> Or am I wrong in believing it's that simple?

Nope... it's that simple.

But let's be honest here: we SHOULD use this approach for ALL of these kinds of assessment, yet we don't. Even in the US, we use things like fingerprint matching, handwriting analysis, drug testing laboratories, DNA analysis, dog sniffs for drugs and so forth in legal cases yet we don't perform independent blinded tests of the accuracy of these tools.

[mattrp]

It’s driven by two things - by the public perception that all bad guys fly coach (a la 911) and by governments seeking to expand the number of biometric means to enforce compliance of all sorts of things unrelated to travel. The irony is that many people who oppose a physical border wall on humanitarian grounds don’t seem to see the perils of virtual walls...such as when a visited country decides to share back my fingerprints it collected at the border with my home country despite legal protections against collecting my fingerprints when I’m inside/entering the home country OR any number of other applications that have nothing to do with border protection or everyday travel... unlike a physical barrier that can do nothing but it’s intended purpose. Sorry don’t mean to make this about borders but I’m trying to make a point that sometimes we use tech we end up creating entire new classes of problems worse than Ones we were trying to avoid... maybe the Amish have it right in this regard?

[sli]

Don't forget hair analysis.

And out of all of those, the only one that actually works is DNA analysis and even that fails from time to time due to how easily samples can be contaminated.

[ergothus]

My understanding is that DNA is basically unique, but the patterns use for conventional DNA analysis are not. While they may be statistically close enough to unique to trust over the whole population, there have been different issues when you start scoping things to different racial groups or areas with smaller gene pools (not dangerously small, just smaller).

Because actually sequencing and comparing someones entire DNA would be prohibitively expensive if done for every case, they just look for a set of markers and assume that a large enough collection is close enough without accounting for distribution patterns of those markers AMONG THE SAMPLE POPULATION. (e.g. you don't have to look hard in small towns or in populations of the same heritage to notice a lot of physical characteristics that are quite common in that sub-population while being pretty distinct in the human population at large, the same is true for these markers.) . Since crimes often involve suspects from the same location and/or racial profile, a rule that is pretty reliable for the earth is not so reliable for this town/community/group of suspects.

So the science is a problem even before you get to human error. The odds of a false match take hits of multiple orders of magnitude.

Note: I'm not qualified to speak on the topic, but I've followed the topic with interest at a layman level for a while - be glad to hear from someone who IS qualified to speak on it to shed more light on why I'm right/wrong.

[bsder]

> My understanding is that DNA is basically unique

It is, in a lab environment with lots of source material.

If you are taking small samples of DNA from terribly dirty places and then amplifying the hell out of it, you get massive amounts of contamination.

Rape kits are "mostly" reliable under most circumstances, but have some problematic edge cases. Swabs from crime scenes, on the other hand, are generally garbage.

[coldtea]

>My understanding is that DNA is basically unique, but the patterns use for conventional DNA analysis are not.

Even if they were, unless it's something like blood DNA after an attacker gets hurt, liquids from a rape, etc. it's trivial:

1) for the culprit to take another's DNA and place it on a crime scene

2) for an innocent to leave DNA at what would later be a crime scene

3) for police (or anyone with access) to add someone's DNA at a crime scene [1]

And the worst thing is, the DNA match then is considered "irrefutable" evidence...

[1] If you (3) is far-fetched, you haven't been following 100 years of police tampering to frame people, even in the USA, and much more in places like Latin America, etc. Just two recent examples:

https://www.buzzfeednews.com/article/melissasegura/detective...

https://www.huffpost.com/entry/baltimore-cop-drug-video-indi...

[Godel_unicode]

Where did you get the idea that print matching is untested...?

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3093498/

https://www.nist.gov/news-events/news/2004/07/nist-study-sho...

https://www.pnas.org/content/108/19/7733.short

[fsh]

The point is that the particular techniques used in court cases are often not verified by any scientific testing. The last sentence of the PNAS paper abstract is: "Examiners frequently differed on whether fingerprints were suitable for reaching a conclusion."

[caseysoftware]

"Examiners frequently differed on whether fingerprints were suitable for reaching a conclusion."

is one of those weasel phrases which - while an accurate statement - means absolutely nothing because first "differing" in an opinion means almost nothing and the word "conclusion" is not defined.

Many people assert the Earth is flat and have detailed explanations on why that is the case, yet they "differ" in opinion too.

If fingerprints stood alone as a single point of evidence for guilty/innocent, I might agree. But it's used primarily as a "we have person A who matches close enough, let's go talk to him" that's useful. Or alternatively, if a fingerprint is one (of many) pieces of evidence that goes into making the case, that's useful. Only the worst cop shows say "the computer matched this guy! It must be him!"

* I was with the FBI on fingerprint analysis and saw the data, processes, etc and how a fingerprint is only a data point (aka clue) within the larger case.. and sometimes it's not enough depending on how many points you match.