A heinous crime has been committed at Vox.
Somebody keeps drinking the single source
Ethiopian yirgacheffe coffee I bring to the
office for myself.
I rounded up five suspects from
around the office and fingerprinted them
to see if I could find a match
from a print I found on my mug.
Is fingerprint analysis reliable enough to
pin somebody to this unspeakable crime,
更重要的是 额 你实际上是怎样操作的？
and more importantly… uhhhh… how do you actually do this?
To help me figure out what the hell,
I’m supposed to do I brought in an expert.
My name is Peter Valentin.
I’m an expert in crime scene reconstructionand forensic science.
A fingerprint is probably the most important piece of information
when we don’t have a known connection between the victim and the offender.
We have to find something that people leave at scenes relatively easily
and something that is unique enough
that finding it and identifying what it is will lead us back to the person.
In order to find a fingerprint,
investigators will either use a physical component
like a powder. So not cocoa powder?
Cool cool cool.
Or a series of chemicals that make a print visible on a surface.
Our fingerprints have ridges and furrows that align to create unique, recognizable patterns.
There is a what’s called a loop right here,
you have ridges that are coming into the pattern
and then coming back out.
Here’s another loop right here.
and there’s whorls and those those three categories alone comprise
at least 95 percent of the fingerprints that are in the database.
Everyone’s fingerprints have unique featuresthat differentiate them from everyone else’s.
For instance this ridge splits into two here
and this ridge has a break in it.
These patterns remain the same throughout a person’s lifetime,
which makes them a powerful identification tool.
My fingerprint is pretty easy to spot.
The pattern looks like a 1998 Chrysler Sebring.
Investigators rely on the characteristics of a print
to find a match using a method called ACE-V.
First they analyze the print and the surface it’s on
to see if it’s viable for examination.
This one’s great.
This one, not so much.
Then, they take the suitable print and compare it against known fingerprints
looking for points of similarities and differences.
For example both these patterns are whorlsand bifurcate right here.
Investigators look at these traits and try to gauge
if there’s enough points of comparison
to declare it a match.
Finally, a qualified peer reviews their conclusion to verify the match.
After using high tech software to analyze the prints from my mug
– I’m kidding this is just some stock footage I downloaded.
I think I finally found a match.
但是 好吧 尽管它是由权威得出
But, ok, even when it’s done by professionals…
how reliable is fingerprint analysis?
It’s a useful tool that obviously has value,
but I think it’s problematic to overstate
its value especially in a criminal justicecontext.
一项精确的研究发现 在1％的情况下 检查员会做出肯定性误检
One accuracy study found that examiners made false positive identifications in 1% of cases.
Which means identifying a print as a match when it’s not.
That doesn’t sound too bad…
unless you happen to be one of those false positives.
布兰登·梅菲尔德 一个俄勒冈州的律师 就是极其不幸的一个
Brandon Mayfield, a lawyer from Oregon, was one of those unlucky few.
He was falsely accused of the 2004 Madrid train bombing
because the FBI made a false
positive match with a partial print foundat the scene.
Mayfield seemed like a good suspect to investigators
because he had recently converted to Islam
and was the lawyer for a man who attempted to join the Taliban,
which in the wake of 911
were all red flags for the FBI.
There was a bias that existed because
once they tentatively identified the unknown fingerprint belonging to this individual
who he was and what his background was made the identification
seem stronger than it actually was.
He didn’t have a valid passport.
So it’s a little implausible on the face of it
that he was handling a bag of detonators in Spain.
Fingerprinting was so powerful that it just sort of it trumped everything else.
Mayfield was even given his own analyst who examined the prints,
and even they agreed
that it was a match.
偏见是一件有趣的事 因为你知道 每个人的假设都是
That’s an interesting thing about biasbecause, you know, everybody’s assumption
is that the experts are biased toward the side that they’re working for.
Here was a guy who was working for Mayfield
and yet he corroborated the evidence against
him which turned out to be incorrect.
The FBI released a 330-page report about where their analysts went wrong,
and it’s pretty much a case study in a lot of the potential downfalls of fingerprinting.
他们列举了一些失误 例如 忽视了指纹间的不同
They cited things such as, ignoring differences between the prints,
lack of independent verification, the pressure
of working on a high profile terrorism investigation,
and letting bias about the suspect affect their analysis.
Their report summed it up by saying
” in any human endeavor, there is a potential for error.”
You know I would suggest learning from history
and realizing that none of these things are going to be error free.
So there’s going to be mistakes and errors andscrew ups.
But also evidence is inherently probabilistic.
So even though it’s not a perfect tool,
until a more reliable technology emerges,
law enforcement will continue to utilize fingerprintanalysis.
And I won’t ever be fully certain of who stole my coffee.
Until I catch him on this new surveillance camera that I installed.