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FBI testimony on hair analysis contained errors in 90% of cases (2015)

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Re: FBI testimony on hair analysis contained errors in 90% of cases (2015)

#41

Post by throwaway74829 »

MerelyMortal wrote: post #33
jacobolus wrote: post #14

Earlier quoted context omitted.

Polygraphs, fingerprints, DNA, face matching, forensic ballistics, forensic psychology, witness testimony (especially police testimony), ...

I'm willing to believe that fingerprints are unique until proven otherwise, though I would need to see the actual finger prints and not some computer report claiming they "match". I also know that fingerprints can be faked.

Fingerprints are unique in the technical sense (i.e. no one has the exact same set of fingerprints) -- but matching is a completely different issue.

I don't know how far forensic science has come since a decade ago when I learned some of it, but at that point they were running "feature matching" instead of full-fingerprint matching. In other words, they looked for aberrancies (e.g. "islands," "deltas," "bifurcations" etc. at specific spots), and then checked those against a finger-to-person database. Then a list of possible matches would be found, if they also contained some set amount of same features in the same places.

There are two main issues here.

First, while taking an optical scan can provide very high-resolution images of a fingerprint -- field data is never like that. Fingerprints that are collected usually are not uniform, and dependent on pressure applied by the finger(s) in question and the amount of oil left behind (which powder sticks to "reveal"). Because of this, you're never going to get a perfect fingerprint in the field. Some areas will be faint, misleadingly separated (and even have false artificial aberrancies not present on the original finger), or outright missing -- leading to less "features" to check against. Others will be completely "blotched" out by a high amount of oil, removing vital information.

Second, you will almost never get an exact match because of this -- you will be getting a list of possible matches. I can remember one notable case of a terrorist's prints being wrongly attributed to someone who could never have been at the scene, much less anywhere near the country -- but was still whisked away by (I believe?) Interpol. Forensic evidence is just a piece of numerous possible stories that can be spun up any which way. There's something to be said here about human biases, incentives, and so on -- but I think it's intuitive enough (and frankly, I don't want to write more).

Re: FBI testimony on hair analysis contained errors in 90% of cases (2015)

#42

Post by thaumasiotes »

beebeepka wrote: post #28
fnordpiglet wrote: post #12

Earlier quoted context omitted.

Or prejudices.

Is there a difference? I am also guilty of this and suspect most of us are Tinfoil on: maybe that's why they were pushing this CSI bullcrap for as long as they did.

Yes, there's a difference.

One is mostly about getting a conviction - of anyone - so that you look like you're doing a good job. This is a real and strong pressure faced by politicians and law enforcement.

Re: FBI testimony on hair analysis contained errors in 90% of cases (2015)

#43

Post by gus_massa »

boomboomsubban wrote: post #31
jacobolus wrote: post #14

Earlier quoted context omitted.

Polygraphs, fingerprints, DNA, face matching, forensic ballistics, forensic psychology, witness testimony (especially police testimony), ...

DNA has a fair amount more credibility than the others. While it's not the silver bullet people think it is, and it can be used to falsely incriminate someone, there is a scientifically supported method of showing two samples of DNA belong to the same person.

IMHO, the real DNA analysis is credible.

The problem is that there are some attempts to make weaker test and try to confuse people so they think it's the real test. For example: https://en.wikipedia.org/wiki/DNA_profiling#Partial_matches

Quoting the Wikipedia article:

> We can see no reason why partial profile DNA evidence should not be admissible provided that the jury are made aware of its inherent limitations and are given a sufficient explanation to enable them to evaluate it.

That sound good, but every time I read it again it looks more and more fishy.

Re: FBI testimony on hair analysis contained errors in 90% of cases (2015)

#44

Post by DebtDeflation »

mkl95 wrote: post #9

Within two weeks I have learnt that bite mark and hair analysis are full of BS. Is there some list of all these shoddy methods?

Drug sniffing dogs that alert to please their handler when he gives them a cue that he wants them to alert.

Re: FBI testimony on hair analysis contained errors in 90% of cases (2015)

#46

Post by DebtDeflation »

mistrial9 wrote: post #32
PicassoCTs wrote: post #19

Earlier quoted context omitted.

Fire "trace" analysis was proven shoddy too.

interesting - links?

https://archive.ph/DJGW7

There's a graphic about halfway down that shows supposed "evidence" of accelerants being used when in fact they're either common to all fires, caused by the rapid cooling from water used to extinguish the fire, or are simply random occurrences completely unrelated to the fire. Yet to this day they are taught to investigators as rock solid evidence of arson.

Re: FBI testimony on hair analysis contained errors in 90% of cases (2015)

#47

Post by [deleted] »

hedora wrote: post #34
ldoughty wrote: post #21

Earlier quoted context omitted.

Firstly, I'm sorry you went through the system and had to face these kinds of issues. I generally agree with you. The fact some of these citizens people were likely incorrectly executed, and others died in prison, based on bad science makes this depressing to read. However, I would factor in intent and knowledge on the part of lab workers and experts when demanding penalties for their action. If they intentionally li…

It's the explicit job of prosecutors to get guilty verdicts regardless of the defendant's guilt. This is the core of the US's adversarial justice system. (In the same way it is the defense attorney's job to get a not guilty ruling.) I think this should be changed, so that false convictions are treated with the same level of seriousness as police officers shooting unarmed civilians on camera. Patterns of prosecutorial…

[deleted]

Re: FBI testimony on hair analysis contained errors in 90% of cases (2015)

#48

Post by bell-cot »

One of our clients at $Job is a testing laboratory for mold & asbestos samples - just from building inspectors & such. To maintain their modest accreditations, every single Analyst (person looking at submitted samples through a microscope) at that lab has to perform daily duplicates & replicates of their own & their coworkers' results (and achieve fairly demanding levels of consistency on those). Then they trade samples with other labs weekly or monthly, to demonstrate further consistency & accuracy of results. Then the accrediting inspectors come through to inspect regularly. Then...

Where the hell were the grown-ups, let alone an inspector who actually understood laboratory QC, when the FBI was running a Keystone Cops clown lab for years?

Re: FBI testimony on hair analysis contained errors in 90% of cases (2015)

#49

Post by boomboomsubban »

djleni wrote: post #40
boomboomsubban wrote: post #31

Earlier quoted context omitted.

DNA has a fair amount more credibility than the others. While it's not the silver bullet people think it is, and it can be used to falsely incriminate someone, there is a scientifically supported method of showing two samples of DNA belong to the same person.

Maybe you know more about this than me, something that makes me uneasy about DNA evidence: Say you can confirm a sample is 100% a certain person. How do investigators have any idea how it got there? How do you know it’s from a criminal and not the guy that stocked the convenience store shelves? I tried to look into this and maybe I was searching the wrong thing but found nothing.

>How do investigators have any idea how it got there?

They often can't be certain, and I'm sure somebody is in prison because they're DNA was in an inconvenient place, but it's a far superior form of evidence than the other methods mentioned.

Unless a crime is widely watched in person with supporting recordings and DNA evidence, it's basically impossible to be a 100% certain of what happened. That's why court only attempts to prove guilt beyond reasonable doubt.

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