Not fingerprinting, but related issue for microscopic hair comparisons:
The Justice Department and FBI have formally acknowledged that nearly every examiner in an elite FBI forensic unit gave flawed testimony in almost all trials in which they offered evidence against criminal defendants over more than a two-decade period before 2000.
Of 28 examiners with the FBI Laboratory’s microscopic hair comparison unit, 26 overstated forensic matches in ways that favored prosecutors in more than 95 percent of the 268 trials reviewed so far
This isn't the case I originally recalled, and doesn't say how many points were matched, but I remember a 5 point match being used to convict a person who was later proven innocent.
Fingerprints aren't "junk science", but they do have error margins and plenty of room for mistakes. The problem is that many juries, judges, prosecutors, and even defenders forget about this.
This is the case for many types of evidence; witness statements for example can also be notoriously unreliable. It's not bad to use this kind of evidence, but you do have a problem if you consider any witness statement to be absolute truth and never consider any "reasonable doubt" there may be, and this is how you end up convicting people based purely on "I saw the suspect commit the crime from 50 metres away in the dark and I'm sure it was him!" or some such.
If you have six independent witness statements like that, or a witness statement and fingerprints then the reasonable doubt starts becoming a lot less reasonable.
This is also the problem with the case in this article: a piece of evidence over which it seems like reasonable doubt should exists is the singular piece of evidence tying this person to the crime. The problem here isn't the evidence as such IMHO, but that juries and/or defenders (depends on the case) seem exceedingly bad at sceptically examining physical evidence.
Fingerprints are directly-recorded facts. What may be junk science is what expert witnesses present about the interpretation of fingerprints.
> The problem is that many juries, judges, prosecutors, and even defenders forget about this.
Juries as triers of fact, and judges insofar as they are ruling on the facts of the case, aren't, in any case, supposed to allow themselves fo be guided by extrinsic knowledge, they are supposed to act based on facts (both direct and the expert knowledge relating to the import of direct facts) provided as evidence, both testimony and exhibits, in the case.
That's not really how it works; false positives exist, especially if you consider that a lot of times you have incomplete or smudged fingerprints and there is actually some amount of subjectivity involved in determining a match. See e.g. [1]: "only two properly designed studies of latent fingerprint analysis had been conducted. These both found the rate of false matches (known as “false positives”) to be very high: 1 in 18 and 1 in 30."
Again: useful evidence for sure, but considering them undisputable facts is not wise.
Matches (positive or negative) are not the same thing as fingerprints. Fingerprints are directly recorded facts. Matches are matters of interpretation (the fact of a match reported by a particular system is a distinct direct fact from the fingerprint itself, but again the significance is...what expert testimony exists to establish or challenge.)
The reality is that when "fingerprint evidence" is brought to court that it's not foolproof and has a sizeable margin of error that should be accounted for when considering the verdict, something that is currently often ignored. You can argue semantics all day, but that's the way things work right now. This seems like an exceedingly pedantic point to make.
> The reality is that when "fingerprint evidence" is brought to court that it's not foolproof
No evidence is foolproof. My entire point is that the issue isn't with “fingerprints” or the knowledge that juries and judges bring extrinsically (which was the explicit claim made upthread), but with the expert testimony that contextualizes fingerprints.
(This was even more clearly the problem with fiber evidence when the FBI crime lab was presenting pure bunk expert testimony in virtually every case.)
Yeah, knowing or not, comparing with too few points is misconduct - that should be the fault of someone besides the defense, but that is somewhat tangential - does anyone with more knowledge know where the line is drawn? I imagine there are some outlandish coincedences happening.
How then do you explain the success of Touch ID on Apple devices and the equivalent systems on other phones and tablets?
Random people can't just walk up and unlock a Touch ID device with their fingerprint, which suggests that fingerprints are in fact a very good way to tell people apart.
Yes, it is possible to make a fake fingerprint that Touch ID will not be able to distinguish from my fingerprint. But that fake fingerprint will only unlock my device, not your device, so it is still correctly distinguishing our fingerprints.
> How then do you explain the success of Touch ID on Apple devices and the equivalent systems on other phones and tablets?
Because on those devices the fingerprint is only used as a second factor (the first factor being physical possession of a particular device).
If Apple used fingerprints like law enforcement do, that is running a fingerprint against the big DB of all prints, then they would certainly get some arbitrary matches.
How many people have you let try the unlock your device with their fingerprint? Tens or hundreds of Millions? That'd be a closer comparison for how a search of fingerprint database work.
Searching a big DB is one way to use fingerprints. It is a crappy way, though.
Another way fingerprints are used is to compare fingerprints found at a crime scene to people who have been identified using other methods that have nothing to do with fingerprints.
E.g., if you have someone murdered in his office when working late at night, and security cameras show that five other people were in the building at the time of the murder, and you are able to get a good set of fingerprints off the murder weapon you don't need a database. You take the fingerprints from all five of those other people, and if one is a very good match and four do not match, you concentrate most of your effort on the one that matched.
It's actually quite similar to how DNA evidence has been used and misused. I don't know how they compare DNA nowadays, but when DNA evidence was first making waves getting people convicted they only compared two DNA samples at a few points. For a given sample there would likely be several people in the country that matched.
That's fine if used right, like fingerprints in the earlier murder hypothetical. Narrow it down to only 5 people who could have committed the crime, get a DNA sample from the crime scene that must be from the criminal, and if that matches exactly one of those 5 suspects it is strong evidence they are the criminal.
Have no suspects yet, run that same sample through a database, get exactly one match, and conclude that must be the criminal. Totally bogus. A lot of people were convicted in the early days of DNA matching that way.
The database method can be made sound, but only if the database includes everybody. Match against a database that includes everyone, only get one hit, and you've probably got your criminal. But if the database includes everyone you are likely to get several matches.
As I said, that was how it used to be. I know DNA sequencing has gotten faster and cheaper over the years, but I have no idea if routine forensic DNA matching now matches enough to make matches unique except in the case of identical siblings.
I'm curious if you think that an accused person could be used to setup a Touch ID, then have the prints collected at a crime scene used to unlock the device.
Do you think the forensic prints would meet the standard required by Touch ID?
Ok, but supposing what you say is true, they are junk science when it comes to forensics. There is research on capturing the full 3D structure of fingerprints to actually capture the uniqueness of a fingerprint[0]. But even if the 2D scan is enough not every scanner is capable of collecting that structure.
Given how much R&D goes into making better fingerprint scanners, it seems odd to then claim that a fingerprint taken off of a victim has anything near that level of detail. I guess its sound to say that it may be used as a piece of evidence to further narrow down the target, but its completely disingenuous to claim that it's sound evidence.
Because other surfaces are not a purpose built sensor designed to detect the features of a finger then repeatedly trained with a specific set of finger scans?
Like are you joking?
Saying TouchID validates fingerprinting is like saying MRI machines validate psychics.
It seems you two have a different idea of what is being discussed. The underlying fundamentals of finger prints are solid. The part that can make them ineffective is when they are using insufficiently tested tools or matching on too few points. And of course misrepresentating what a match actually means and how it pertains to the case.
> The underlying fundamentals of finger prints are solid.
What exactly are these underlying 'fundamentals'? Nobody even knows if everybody has unique fingerprints, it's just an assumption.
Beyond that, it's not all that relevant since as you mentioned how the matching is done is largely subjective, and it depends a lot on the number of "points" used and who does the matching, and that should really bring the accuracy even more into question. What exactly is the statistical probability of an incorrect match based on the number of points used? Good luck answering that question.
IMO the situation is made a lot worse by the fact that the public generally assumes fingerprinting to be extremely accurate (or 100% accurate).
