7 ms·

fiber analysis is also fake as hell (like saying: these threads came from your carpet, or your shirt). ballistic forensics only works if the gun is barely fire

fiber analysis is also fake as hell (like saying: these threads came from your carpet, or your shirt). ballistic forensics only works if the gun is barely fired after the time that the bullets in question are fired, becuase each time you fire a gun it wears down the barrel again, in new ways. Fingerprint analysis is not based on solid science, nobody knows how common it is for someone to have very similar fingerprints to another person, and nobody knows what the right standard for "points of similarity" is. Fingerprint analysis has been used to convict people of crimes they could not have committed because they were not in the same state or even country, in ways that are provable: https://en.wikipedia.org/wiki/Brandon_Mayfield https://en.wikipedia.org/wiki/Brandon_Mayfield

derefr 4y ago
> fiber analysis is also fake as hell (like saying: these threads came from your carpet, or your shirt). I'm not a forensic technician, but I've watched probably every episode of every true-crime forensic documentary TV show / YouTube channel / podcast / etc that exists; which probably has some weak but non-negligible correlation with having a gestalt impression of what people do and don't use forensic techniques for in practice. (At least in the "solved" cases, since the point of these shows is "how they solved it.") In every use of "fiber analysis" I ever saw covered, where the "fiber analysis" was actually used to prove something, the thing they're always noticing is "trilobal fibers" — presumably because, at least for some period in recent history, those type of fibers only ever got used by specific manufacturers for specific use-cases (vehicle manufacturers, for car floor matting, IIRC); and weren't part of the composition of anything sold to individuals at retail (except, perhaps, replacement car floor mats.) So "trilobal fibers on the body" could be taken to imply "this person was at some point in a car footwell/trunk." I don't ever recall any case that made a "fiber analysis" claim other than that particular one. (Maybe once someone claimed something about what proprietary dyes were used on the fibers via GCMS assay — but that's not really "fiber analysis" per se.)
- giantg2 4y ago
  I don't have a link handy, but there was a huge FBI scandle where their experts were essentially calling things a match to a specific person, etc. But yes, the science is fine if interpreted correctly. The correct phrasing would be exclude or not exclude a suspect. Or for your example, it could be consistent with someone having been in a vehicle. The problem is when the experts say they must have been in a vehicle, or especially a specific individual vehicle.
  - Ekaros 4y ago
    That seems something that should be criminal. And realistically always asked how many vehicles with this type of material is there around?
  - WaitWaitWha 4y ago
    The judge should have thrown it out. Second thing they teach in forensics is that unless I witness the actual event, it is really hard to tie it to a specific person. I can present dozens and dozens of circumstantial evidence which has sufficient weight for a reasonable person to make that inference, but I cannot attest to that.
    - giantg2 4y ago
      Judges should do a lot of things. In reality, their quality and knowledge varies greatly.
      - wahern 4y ago
        Any judge worth their salt would prohibit or censor witness testimony making conclusory statements, especially based on circumstantial evidence. This is Evidence 101. Everybody knows the so-called "hearsay" rule, but almost every rule in evidence revolves around one core precept--no evidence is per se conclusive, and the function of testimony of any sort isn't to submit conclusions to the question at issue. But implying conclusions is exactly what both the defense and prosecutor are working at; they're constantly playing word games, and some judges would certainly be better than others at seeing through the B.S.
bornfreddy 4y ago
Thank you for the link! Though I would say it highlights a different problem (investigators' bias) than stated. The Spanish police have rejected findings apparently.
thrdbndndn 4y ago
> nobody knows how common it is for someone to have very similar fingerprints to another person Your last example is definitely a good counterexample to this, but I feel in most of cases, the suspects are very few so fingerprints only need to be able to distinguish one of the others, than say, identify a random dude from billions. So it's still useable. It's like while SHA-1, or even CRC32, is totally incapable for security, it's still perfectly fine to be used to detect if a known file is corrupted (through natural cause, not deliberately altered) or not.
- jrochkind1 4y ago
  That's like saying if a witness says "he had brown hair, that's all I can say", and only one of "the suspects" had brown hair, that's reason to convict him.
  - Eisenstein 4y ago
    You are misrepresenting the odds of a group of people having an outlier hair color vs a group of people having one which matches sufficiently well to a piece of evidence which excludes the others. 'I remember a brown car' vs "I remember a brown 1976 Ford coupe with worn tires and a broken side window'.
    - pas 4y ago
      please don't forget all the databases that can search for fingerprints, and all the suspects brought before the detectives, and at that point if they did not have a good enough alibi, or good enough psyche to withstand interrogation, or ...
      - dsfyu404ed 4y ago
        https://en.wikipedia.org/wiki/Brandon_Mayfield https://en.wikipedia.org/wiki/Brandon_Mayfield
        deleted 4y ago
WaitWaitWha 4y ago
Forensics evidence is almost always circumstantial. For your example - If everyone wears wool sweaters except one person wearing poly microfibre, what is the inference? The first rule that is taught in forensics is that every interaction leaves a trace of some sort. The poly microfibre showed up at the scene. How did it get there is now a different type of forensics and where lawyers step in. The prosecutor will insist because the poly microfibre owner was there, while the defense lawyer will insist, there was a party the night before and everyone was rubbing against each other, the poly microfibre wearer and the wool sweater wearers. It can be anyone.
shusaku 4y ago
> Fingerprint analysis is not based on solid science, nobody knows how common it is for someone to have very similar fingerprints to another person, and nobody knows what the right standard for "points of similarity" is. Weird, I mean surely we have enough data to answer these questions with high certainty? Makes you worry that somebody won’t like the answer…

derefr 4y ago

> fiber analysis is also fake as hell (like saying: these threads came from your carpet, or your shirt). I'm not a forensic technician, but I've watched probably every episode of every true-crime forensic documentary TV show / YouTube channel / podcast / etc that exists; which probably has some weak but non-negligible correlation with having a gestalt impression of what people do and don't use forensic techniques for in practice. (At least in the "solved" cases, since the point of these shows is "how they solved it.") In every use of "fiber analysis" I ever saw covered, where the "fiber analysis" was actually used to prove something, the thing they're always noticing is "trilobal fibers" — presumably because, at least for some period in recent history, those type of fibers only ever got used by specific manufacturers for specific use-cases (vehicle manufacturers, for car floor matting, IIRC); and weren't part of the composition of anything sold to individuals at retail (except, perhaps, replacement car floor mats.) So "trilobal fibers on the body" could be taken to imply "this person was at some point in a car footwell/trunk." I don't ever recall any case that made a "fiber analysis" claim other than that particular one. (Maybe once someone claimed something about what proprietary dyes were used on the fibers via GCMS assay — but that's not really "fiber analysis" per se.)

giantg2 4y ago
I don't have a link handy, but there was a huge FBI scandle where their experts were essentially calling things a match to a specific person, etc. But yes, the science is fine if interpreted correctly. The correct phrasing would be exclude or not exclude a suspect. Or for your example, it could be consistent with someone having been in a vehicle. The problem is when the experts say they must have been in a vehicle, or especially a specific individual vehicle.
- Ekaros 4y ago
  That seems something that should be criminal. And realistically always asked how many vehicles with this type of material is there around?
- WaitWaitWha 4y ago
  The judge should have thrown it out. Second thing they teach in forensics is that unless I witness the actual event, it is really hard to tie it to a specific person. I can present dozens and dozens of circumstantial evidence which has sufficient weight for a reasonable person to make that inference, but I cannot attest to that.
  - giantg2 4y ago
    Judges should do a lot of things. In reality, their quality and knowledge varies greatly.
    - wahern 4y ago
      Any judge worth their salt would prohibit or censor witness testimony making conclusory statements, especially based on circumstantial evidence. This is Evidence 101. Everybody knows the so-called "hearsay" rule, but almost every rule in evidence revolves around one core precept--no evidence is per se conclusive, and the function of testimony of any sort isn't to submit conclusions to the question at issue. But implying conclusions is exactly what both the defense and prosecutor are working at; they're constantly playing word games, and some judges would certainly be better than others at seeing through the B.S.

bornfreddy 4y ago

Thank you for the link! Though I would say it highlights a different problem (investigators' bias) than stated. The Spanish police have rejected findings apparently.

thrdbndndn 4y ago

> nobody knows how common it is for someone to have very similar fingerprints to another person Your last example is definitely a good counterexample to this, but I feel in most of cases, the suspects are very few so fingerprints only need to be able to distinguish one of the others, than say, identify a random dude from billions. So it's still useable. It's like while SHA-1, or even CRC32, is totally incapable for security, it's still perfectly fine to be used to detect if a known file is corrupted (through natural cause, not deliberately altered) or not.

jrochkind1 4y ago
That's like saying if a witness says "he had brown hair, that's all I can say", and only one of "the suspects" had brown hair, that's reason to convict him.
- Eisenstein 4y ago
  You are misrepresenting the odds of a group of people having an outlier hair color vs a group of people having one which matches sufficiently well to a piece of evidence which excludes the others. 'I remember a brown car' vs "I remember a brown 1976 Ford coupe with worn tires and a broken side window'.
  - pas 4y ago
    please don't forget all the databases that can search for fingerprints, and all the suspects brought before the detectives, and at that point if they did not have a good enough alibi, or good enough psyche to withstand interrogation, or ...
    - dsfyu404ed 4y ago
      https://en.wikipedia.org/wiki/Brandon_Mayfield https://en.wikipedia.org/wiki/Brandon_Mayfield
      - deleted 4y ago

WaitWaitWha 4y ago

Forensics evidence is almost always circumstantial. For your example - If everyone wears wool sweaters except one person wearing poly microfibre, what is the inference? The first rule that is taught in forensics is that every interaction leaves a trace of some sort. The poly microfibre showed up at the scene. How did it get there is now a different type of forensics and where lawyers step in. The prosecutor will insist because the poly microfibre owner was there, while the defense lawyer will insist, there was a party the night before and everyone was rubbing against each other, the poly microfibre wearer and the wool sweater wearers. It can be anyone.

shusaku 4y ago

> Fingerprint analysis is not based on solid science, nobody knows how common it is for someone to have very similar fingerprints to another person, and nobody knows what the right standard for "points of similarity" is. Weird, I mean surely we have enough data to answer these questions with high certainty? Makes you worry that somebody won’t like the answer…