Thank you guys so much for bringing your questions and comments. This has been a great response and we were so happy to share our perspective with you all. We hope that this was interesting to you guys as well and hope that you also find out podcast interesting whether we're talking fingerprints, forensics, or cases. We'll be bringing many of these questions to our wrap up episode of MaM on the 22nd. If you have anything that we missed, send it in or message us and we'll try to answer it on the show.

Thanks again, DLP

Eric Ray (u/doubleloop) and Dr. Glenn Langenburg (u/doppelloop) are Certified Latent Print Examiners and host the Double Loop Podcast discussing research, new techniques, and court decisions in the fingerprint field. They also interview forensic experts and discuss the physical evidence in high-profile cases.

Ask us anything about our work or our perspective on forensic science.

r/MakingaMurderer, r/TheStaircase, r/StevenAveryIsGuilty, r/TickTockManitowoc, r/StevenAveryCase r/forensics

Proof -

Comments: 464 • Responses: 49  • Date: 

SecondaryAdmin23 karma

Based on your experience, would you say a guilty Steven Avery was quite competent in removing evidence of his crime or quite sloppy in leaving the evidence he did? Would it have been plausible for a person who was close to him to have planted the evidence that was found, such as the bullet, the key, and his blood?

As a follow up, would you generally agree with the prosecution narrative of how Teresa Halbach was kidnapped, tortured, and killed, based on the evidence, or would you see as something different, say as an unintended moment of rage?

DoubleLoop14 karma

Wow. Good questions. I'd go with a combination of sloppy and careful. Careful everywhere except the RAV4. That might be explained if he had Dassey or some other accomplice hide that while he took care of the burning.

Plausible to plant all that evidence? No. Planting DNA evidence is terribly risky. There's no way to know for sure if you accidentally also incriminated yourself.

Agree with the narrative? No. I don't think she was stabbed or cut in the bedroom. It seems much more plausible to me that something led to Avery attacking her and then the rest was getting rid of evidence.

Adamarama3 karma

I dunno, I don’t think many people would understand the risks of getting their own dna mixed up, if the were just say holding a swab to a surface. if it was a cop who planted it and was also involved in investigating and their dna was found as well he could just say oops must’ve happened at the crime scene or somewhere along the line. It doesn’t seem out of the realm of possibility.

DoubleLoop2 karma

But it wasn't just planting of one piece of evidence. It was lots of evidence that would have been planted. And a cop could shrug off his own DNA being mixed in, but that wasn't found in this case. And it probably wasn't just covered up, because other contamination from the DNA analyst wasn't covered up. It was a big part of this trial.

Could I imagine a perfect scenario where everything went perfectly for the planting to occur and no evidence of the planting left behind? Sure. But Avery being the killer seems to me to be a much more likely scenario to imagine.

TheRainforestSucks18 karma

Do you believe the amount of prints found in TH RAV4 were a plausible amount of prints to discover? Or in your opinion, were there a suspiciously small (or possibly large) amount of prints discovered.

DoubleLoop36 karma

The number of prints on the RAV4 fall very much into the range that we typically see. Fingerprints on interior surfaces of vehicles are quite uncommon (with a couple of exceptions like the windows and mirrors).

puzzledbyitall18 karma

In the Avery case, I often hear Avery supporters say that renowned experts would not sacrifice their reputations by saying anything that could not be supported by good science. Is this true in your experience? For example, I have no doubt that James is an well-qualified blood spatter expert. . .but I find his suggestion that because blood is not on door handles, the steering wheel and the like, it must be planted to be ridiculous.

DoubleLoop31 karma

Good question. Glenn is trained in bloodstain pattern analysis and recognizes James's expertise. He was also confused by that comment. We can only theorize that the question asked of him was phrased as "Wouldn't you expect blood to be on the handle if it was touched by someone who was actively bleeding?" The show is edited and may have left that part out.

Right now we trust his expertise and then are wondering why he would say something that's so obviously incorrect.

puzzledbyitall19 karma

Thanks! Do you find that experts seem to worry about their reputations when they file affidavits? My guess is they figure their reputations are based on their scholarly articles and books, and that most people don't read affidavits.

DoubleLoop20 karma

Not quite.

More that experts testify to their opinions based on their findings, and try to phrase these very carefully so as not to overstate anything. Experts in the accepted forensic sciences aren't normally interested in saying anything unsupported no matter who hires them.

H00PLEHEAD15 karma

What are your thoughts on the "CSI effect", and do you think it has impacted the expectations of viewers of Making a Murderer 1&2?

DoubleLoop22 karma

For years now, I've had to go and testify at trial when I didn't find any fingerprints at all. Prosecutors have learned that if there isn't any physical evidnece, the jury still wants to hear that the scientist tried. They're not comfortable just taking the officer's word for it.

After recently engaging with the online communities that are actively discussing MaM and The Staircase, I think the biggest problem is that people are WAY overvaluing certain evidence that is only weak, and then WAY WAY overvaluing other evidence that is just inconclusive. The lack of fingerprints inside the RAV4 is often pointed to as evidence that the car was wiped down. And then with blood also there, it's evidence that it was all planted. This just isn't the case. A lack of fingerprints on an object that was touched is common, especially the interior of a car.

H00PLEHEAD7 karma

Thank you.

As a follow up, and forgive me if you've addressed this elsewhere, what are your thoughts on the adage:

The absence of evidence is not evidence of absence


DoubleLoop16 karma

Usually holds true, but there are some exceptions. It mainly depends on the circumstances of the case.

For example, absence of an entire car is evidence of a stolen car.

desertedlacuna12 karma

What is most misrepresented about your work in media?

DoubleLoop30 karma

On TV shows the main thing they get wrong about latent print analysis is that it's all done by computers. While AFIS is a critical tool to search through millions of records, the final decision is made by a human examiner.

In forensics in general, it seems that people seem to over value certain pieces of forensic evidence and also to over value the lack of physical evidence as meaning something

TragicallyHopeful11 karma

If a cadaver dog follows a scent and hits on an area, how likely is it that a body is or was in that location versus a false positive?

In other words, is it common during a large search effort for cadaver dogs to have 1 or a couple bad tracks with false positive hits? Maybe even 2 dogs following the same scent even.

Some people suggest that a hit is a guarantee that a body is or was there, and I personally can't see that being true.

DoubleLoop6 karma

I haven't done much reading into the accuracy of scent dogs, but from a couple of articles it's clear that their accuracy isn't 100%.

Also, I think that they can track someone if their possessions or blood go into an area, and not necessarily the person themself.

watwattwo10 karma

At least one of you mention that you think Zellner does a great job poking holes and bringing up reasonable doubt. Of course, you are only hearing Zellner's side on a show intended to bolster those arguments, and I believe you've both agreed that her theories and conclusions are absurd.

IMO, given all of the evidence against him, no reasonable theory exists where Steven is innocent - they all require numerous bad actors working in tandem (despite no motive nor evidence) along with ridiculous coincidences on Steven's part. There may be reasonable doubt about how Steven did it, but IMO there's no doubt that he did do it.

With that said, if you were a juror on a hypothetical retrial (thus also hearing the state's rebuttal to Zellner), do you believe you'd find Steven guilty?

DoubleLoop21 karma

I think we'd both say guilty if we were jurors in a retrial. I think Glenn's point when he made those comments was to say that Zellner was doing a good job raising reasonable doubt, and that it may be effective with some jurors. Most jurors don't have the science background that we have and may be convinced by some of her arguments.

puzzledbyitall8 karma

Is it true that tests for prints often makes it difficult or impossible to test the same material for dna?

Also -- and this relates to a personal situation -- if dna is detected, but there is insufficient dna to create a profile, does that mean the results are useless?

DoubleLoop14 karma

In most cases, examiners will have to decide whether to swab for DNA (and rub off any prints) or to process for prints (and cover up DNA with chemicals or powders or tape).

Fortunately, textured surfaces are great for DNA and terrible for prints. Smooth surfaces are the opposite.

It's therefore common to swab the grip areas of a gun and leave the smooth slide for latents.

Also---- Not necessarily useless. An expert looks at the height of the peaks that indicate different loci. If the peaks are too low, then they are not considered. It's technically possible to ignore that limit and look at the peaks that are lower, and you may glean additional info, but there becomes an increased risk that you're reading noise and not actual DNA

liveandletdeepfry8 karma

What did you think of the 'saliva DNA' from MAM S2?

doppelloop3 karma

Is this in reference to the DNA on the latch of the hood (Avery's) or the DNA on the bullet fragment (Teresa's)?

liveandletdeepfry3 karma

Latch of the hood. Sorry, I meant sweat dna!

DoubleLoop33 karma

The doc tries to insist that there was "too much" DNA on the hood latch. From the published research that we reviewed and discussed in the show. The amount of DNA falls well within the expected range.

As for planting, we just can't understand how backwoods cops could collect and preserve DNA evidence and confidently plant it without getting their own DNA in the sample and confidently knowning that the sample never contained someone else's DNA. And why they wouldn't also plant Dassey's DNA. And why not just plant somethiing less risky.

besimbur7 karma

Forensically speaking, what is your opinion on the evidence against Steven Avery? If you've seen MAM2, could the theory KZ presents be correct? If evidence was planted, could that be proven or is that notion baseless?


DoubleLoop14 karma

We just put out our second episode regarding S2 of the show.

In short, we find some of the new evidence compelling. Sepcifically, the blood spatter by James, the trace analysis by Palenik, and the Brady violation question regarding Bobby's computer logs.

However, we also find the conclusions that Zellner reaches from this new evidence to be totally unsupported by that new evidence. We find no physical evidnece supporting planting, and that the risk of planting going wrong for the officers tooo high for them to even try it.

Standophish7 karma

In Making A Murderer II, did you find Kathleen Zellner's experiments to be based on sound scientific principles, or was she trying to lay it on thick?

DoubleLoop19 karma

Some good and some bad.

The experiments performed by James and Haag and Palenik were good. But they were to some degree done with certain assumptions.

The ones performed just by Zellner and Co. were pretty ridiculous. I'm thinking of the blood near the ignition test, the hood latch test, the recreation with Bobby as the killer test, etc.

The biggest issue is that she jumps to insane conclusions. Since the bullet didn't go through bone, then Avery didn't shoot her. Since the blood stain is castoff, then Avery didn't kill her.

DoubleLoop7 karma

Thought that I'd share my fingerprint artwork page here as well. Let me know what you think

super_pickle5 karma

What is the strangest thing you've ever been able to lift a print from? My understanding is that prints are fairly uncommon, and a lot of surfaces are pretty difficult to get a print from. I've read cases of examiners using novel techniques to get prints from unexpected places.

Have you ever had an exciting find, where you didn't think there was any chance of getting a print?

DoubleLoop9 karma

Prints aren't "uncommon". But they can be moreso on guns, bullets, and the insides of cars. Plastic bags, paper, bottles, and cans are pretty good for prints.

Let's see: Got good prints off brass knuckles. Saw a coworker get a good print off a tree branch. Another from a crossbow. I think the most exciting ones are on triggers. I've found 5 or so there over the years. Another one was on a really thin glass tube from a bong. Didn't expect that print or for it to be identifiable.

H00PLEHEAD5 karma

Do you find attorneys generally misrepresent or dress up your words and findings in their submissions? Do you find Zellner repeatedly doing so to to be indicate of anything, and, if so, what?

DoubleLoop14 karma

Maybe not generally or all the time, but it does happen. I had a conclusion once where I said "inconclusive, but there were similarities to the suspect". Defense kept repeating inconclusive, and I would have to add in that there were some similarities. Prosecution kept talking about similarities, and I had to keep adding in that I was overall inconclusive.

She's a zealous advocate for her client and not beholden to only present scientifically supportable statements.

LordEew4 karma

Do you believe that the amount of blood found at the bottom of the staircase matches with that of a fall?

DoubleLoop13 karma

Probably not, but it's not the amount of blood that is particularly convincing in this case. It's the blood spatter that traces back to an area away from walls and stairs. This is strong evidence that something was swung and hit her.

TragicallyHopeful5 karma

Do you think the prosecution made a mistake handcuffing themselves to the blowpoke?

DoubleLoop19 karma

It's always a mistake to handcuff yourself to a blowpoke.

But seriously, I would have to say yes. Without such an emphasis on that blowpoke, it probably would have been possible to retry him and convict him a second time.

On the other hand, they got the conviction in the first place so it wasn't a terrible idea.

scienceisprettycool-4 karma

Is there any way to "age" a print, to determine how how long ago it was left behind?

DoubleLoop9 karma

Short answer, no.

However, there is new research looking into how different compounds in the residue change over time. Even if that research pans out, it would still only be able to give a range of probabilities due to the variations in the compounds in different people's residue and the variations in environmental conditions.

geographical_data4 karma

What's the most porus surface you've found a useable print on?

DoubleLoop13 karma

Porous evidence can actually be a very good surface for fingerprints. I commonly find identifiable fingerprints on paper and cardboard. Less often, but still possible on currency or even wood.

Amino acids from sweat soak into the porous surface and stay there. A chemical like ninhydrin will react with the amino acids and become visible (purple).

imaginexus4 karma

Do you believe there is some truth to Dassey’s confessions? He does make some surprising links to the real evidence, like his bleached jeans after he confessed to using bleach to clean the blood, or correcting the officers when they bluffed and said Teresa had a tattoo, or admitting to the stabbing but absolutely refuting that he shot her. If you assume he’s at least somewhat guilty, it would make sense that his confession is a mess since he would be telling lots of lies at first to throw them off.

DoubleLoop12 karma

There might be sometruth to the confession. However, I also think the confession should be tossed. Without that there isn't enough evidence to convict

coalwhite4 karma

Haven't seen this question; what is the common academic path one must take to become a forensic scientist, or generally anything forensically related? My kid sister has decided to study anthropology, saying it will get her there. I have my doubts, but what do I know.

DoubleLoop11 karma

Anthro might be a tough way into the field, but it depends on what she wants to do with it. Traditionally, get a degree in chemistry, biochem, or forensic science with at least 30 hours of chemistry classes. Then apply to every opening in the country and take whatever gets offered to you. Once you're in, it becomes much easier to move into the sub-discipline that you're interested in. But you also might just find that you really love something that you didn't know about. I never knew that I would love fingerprints this much. I even make artwork:

TragicallyHopeful4 karma

The recovered bullet fragment is said to have had wood particles but no bone particles.

Could this be consistent with a bullet that traveled through soft tissue only or only grazed the victims flesh and made contact with the plywood walls or wood framing of the garage before ultimately falling to the ground?

DoubleLoop18 karma


And WAY more plausible than chapstick.

mindsetzero3 karma

Then how does this explain that the forensic anthropologist said the skull had bullet markings on it? This was the one thing that LEO's kept trying to get BD to say in his "confession" and had to come out and ask him "who shot her in the head" how would they know she was shot in the head IF the bullet only hit soft tissue and no bone/skull as their "expert" said?

DoubleLoop14 karma

Easy. More than one bullet.

One in the head that was never found, and at least one that went through her, picked up DNA, and was found under the compressor.

pandaaadrew4 karma

Are there any cases that you would say were major turning points for forensic sciences? Like cases that were the first to utilize techniques and tools that are commonly used today.

DoubleLoop5 karma

We're actually going to do an episode on the Night Stalker, RIchard Ramirez soon. That was one of the very first high-profile cases where AFIS technology assisted in identiyfing a fingerprint.

The story of how Ed German brought superglue fuming to the US from Japan is also kinda cool. (And Ed is a really great guy.)

Francisca Rojas case from Argentina.

There are quite a few cases involving DNA from the 80s and 90s that were the beginnings of that field

wheeliedave4 karma

Probably a silly question but just wondered, how much actual human involvement is there in examining fingerprints. In other words, is automation/computerisation going to take over this field? Great podcast btw!

DoubleLoop7 karma

Humans are doing basically all of the work, however, there are new technologies coming into the field that are making things easier.

AFIS has been a fantastic tool that can quickly search through millions of cards to find the prints that look the closest. The system gives the examiner the prints with the highest similarity scores, but then the examiner must review and compare each of those candidates. Most of the hits come in that top score. But about 65-80% of AFIS searches do not result in an identification.

Other technology like on-screen comparison software, tools to search for features., and tools to measure the level of similarity are helping, but still require the examiner to be involved the whole time.

One aspect that is being taken over by computers is tenprint comparisons. That's when someone is arrested or printed, and all 10 fingers are available to be compared. The computers do very well when they have that level of information.

greedyverticalsmile3 karma

In the staircase, I ended up thinking that instead of a blowpoke, he might have grabbed her by the hair and slammed her head on the ground, hard enough to break the skin of her scalp but not so hard that it fractured her skull. I thought he would have raised her head up to just such a height that would have explained all the blood that was supposedly coughed onto the wall at the turn at the base of the stairs.

Do you think the cast off patterns, and the blood on the inside of his shorts, would have supported that idea at all?

DoubleLoop2 karma

Not quite. When we interviewed Bart Epstein, I asked him that exact question. He said that the pattern came from impact with her head. It doesn't match her head just hitting the wall lot the stairs or her head being brought up quickly. At the very least, it had to have come from his hand, fist, or another object impacting on her head.

pangolinsarecool3 karma

What’s the most smoking gun evidence you’ve ever been able to provide?

DoubleLoop5 karma

Print on a trigger.

Another guy claimed not to have had a gun. Cops found a gun in the alley that he had come out of. I found similar characteristics on the magazine from the gun to his finger.

pangolinsarecool3 karma

Wow. I’m guessing handles don’t take prints so well due to texture?

DoubleLoop4 karma

Exactly. Usually the things that you're supposed to hold on to are designed to be textured so that you can hold it better, and so that unsightly fingerprints aren't left behind.

pangolinsarecool3 karma

Fingerprints once revolutionised criminology. Then DNA. What’s the next frontier?

DoubleLoop10 karma

It seems that one of the biggest fields to get into now is computer forensics. We all carry a portable super computer in our pocket that tracks our every location and interaction. Serious questions have to be addressed as to who can access that data and when and why. To balance the public good of locking up violent killers vs. am individual's right to privacy

Nem3213 karma

Opinion of Deaver’s testing methods in the MP case?

DoubleLoop3 karma

u/doppelloop can comment better on that, and he stepped away for a minute.

My understanding is that some of his testing methods were standard for the field, but that some of them were incomplete. Recreating the conditions for blood in the crotch area weren't bad but should have also included tests to see if the same could happen by just checking on the body. His conclusion that the blowpoke matched the head wounds were over-reaching

Nem3214 karma

Thank you, it’s a shame he lied about his experience or MP would still be incarcerated where he belongs.

DoubleLoop3 karma

True dat

Thad_The_Man3 karma

One thing I keep hearing is that if TH were shot or stabbed she would have bleed all over the place. Assuming that no veins or arteries were cut, how much does a stabbed or shot person bleed? Also consider the differences in your answer for a shot when the bullet exits and does not exit.

DoubleLoop14 karma

The short answer is that it can vary quite a bit. I can imagine her death involving a lot of blood or a little bit. Either way, it would be easier to clean up if it occurred on dirt instead of inside the house. To us, it seems more likely that she wasn't killed in the trailer, and maybe not even in the garage. It''s still possible for both, but outside seems more likely.

yaboi2753 karma

Hi, my name is Ash what are some of the procedures you take as to ensure not to contaminate the evidence?

DoubleLoop4 karma

It depends on the evidence. For fingerprint evidence I just wear gloves to prevent my prints from getting onto the evidence. If it needs to be swabbed for DNA, then I'm putting on a lab coat, gloves, and a mask and also decontaminating the counter with bleach. For firearms they make sure not to add additional scratches onto the sample. For toxicology they make sure to glove up to prevent contamination the blood samples but also to prevent exposure to the blood.

iwentupupup2 karma

What kind of microscope were they using in season 2 episode 8? Some kind of cool 3D digital scope?

DoubleLoop3 karma

Was that the one with Palenik? Not sure but def cool

choosetango2 karma

I have heard it claimed that there is no evidence that all fingerprints are unique. What are your thoughts on this?

DoubleLoop3 karma

There's no way to prove that fingerprints are unique, but we don't really have to. There is overwhelming evidence to support that fingerprints are highly discriminating. It's extremely unlikely for two people to have the same print or even the same features on an area of their finger. But there isn't some cosmic registry that once a fingerprint is formed, all other people are forbidden from having that pattern. It's just microscopically unlikely. Like flip a coin every second and get heads for the rest of your life unlikely. Possible? But it's just not gonna happen.

But the real question is can experts ever mistake one person's fingerprint IMPRESSION for another person's fingerprint IMPRESSION. Once it's an impression, a copy, then there are distortions and other problems introduced. Research is really clear that those mistakes can and have happened but they are quite rare in accredited labs with proper quality assurance procedures.

CypripediumCalceolus2 karma

The Chinese are claiming they can identify you on surveillance cameras from how you walk. What about that?

DoubleLoop6 karma

Gait analysis. I've seen it at conferences but don't know much about it. It's a thing, but I need to read more to find out its accuracy

KaraMiller43812 karma

I’ve heard people have disputed Sherry Culhane’s statistics on the tissue DNA found. People have said she presented “guess work” as irrefutable evidence. With 7/15 markers in that DNA how likely is it that the DNA matches Teresa Halbach. Were her statements correct that you would only find that much of a match in 1/1 billion people? Also, I have heard the teeth fragments being matched was incorrectly presented statistic wise. Can you offer some insight into those findings by the prosecutions experts?

DoubleLoop10 karma

Without getting too deep into DNA stats (which would be going a bit far out of my specialty), Teresa's DNA was on that bullet fragment.

Now, there could be many many ways that the DNA could have gotten there. That includes the bullet went through her or that her blood landed on the bullet outside and then was kicked into the garage.

I haven't looked into the teeth fragment evidence enough to comment on that

mindsetzero2 karma

Wasn't it 7 of 13 loci? I just placed a link to some of the lab results in my comment just now as well, wanting to discuss the bones.

DoubleLoop3 karma

I'd have to double check. I thought it was all but 2 loci.

imaginexus2 karma

If someone is wearing gloves during a crime and is cut on the finger through the glove, would we see similar evidence to what we see in Halbach’s vehicle? I’m speaking of no fingerprints from Steven at all, but drops of his blood still in several places, and his sweat DNA but no fingerprints under the hood.

DoubleLoop11 karma

Yes, but... It also all fits what would be expected if he wasn't wearing gloves and then tried to keep his bleeding finger wrapped in his shirt most of the time he was in the car.

There are lots of scenarios that could fit the evidence

makingacanadian2 karma

What are the chances that a scent tacking dog tracking Teresa Halbach specifically, as well as a cadaver dog searching for human remains could both make the mistake of leading their handlers to a bag of decomposing peat moss??

DoubleLoop4 karma

No idea.

Not zero?

hillo5382 karma

How different are the skill sets needed to run a podcast vs the skill sets needed to become a forensic scientist, is there any overlap? What is one thing you that you wish more people would know about their fingerprints?

DoubleLoop4 karma

Well, being a forensic scientist can definitely require a broad set of skills. The one that probably comes in most handy when creating podcast episodes is patience. Editing audio takes time and care. Comparing fingerprints gets you looking and searching for small details through vairous types of noise.

What to know: - you don't always leave fingerprints when you touch something. - it's a skilled examiner that compares fingerprints, not the computer

my-little-throw_away2 karma

Is there any reason why TH's DNA wouldn't be on the key fob? Or a lack of SA's blood in the fibres?

DoubleLoop11 karma

The article that I linked to earlier and the struggle that we mentioned in our show both include 0 as a possible amount of recoverable DNA from a touch. Also, it's more likely that only the last person to touch something had detectable DNA. That can be because DNA in a mixture is only findable if the mixture is relatively close in amount. If one person's DNA is way higher, then the lower DNA is overpowered and not seen.

greedyverticalsmile2 karma

No forensic background at all here, but I thought the blood spot beside the steering wheel in halbach's vehicle looked almost like someone wiped it on with a qtip. There is the main round spot and then a smear tail that appears to point upward rather than down as if in defiance of gravity.

Did that spot look to you like it dropped from a cut onto the dash panel? It didnt strike me as looking like a drop. If not, how would you analyze that spatter--how would that blood have made that pattern?

DoubleLoop13 karma

That stain was a contact transfer. Not a drip and not a spatter. The shape of it is not specific enough to reach any reliable conclusion as to the source. The shape could just as easily have come from Avery as a swab.

However, obtaining enough blood to drip some in multiple places, swab some onto the dash, and then also leave a flake of dried blood under the center console is pretty unlikely. In my opinion

cuthman992 karma

Three questions:

  1. Can you comment on your threshold degree of certainty required before you conclude a latent and a known print are a match?

  2. The National Academy of Science and other experts have strongly urged that a high degree of subjectivity, which leads to serious potential for cognitive bias problems, is a significant and pernicious issue in friction ridge analysis. When you examine a fingerprint in a forensic matter, how much extraneous information about the circumstances around the recovery of a fingerprint are you given prior to making the examination? How are you able to prevent such information from contaminating your opinion about a match?

  3. Have you ever been subjected to blind/secret auditing of your own work? For example, have you ever had the same two prints re-submitted for analysis to you (without warning you they were the same), in order to see if you reach the same conclusion you had on a previous occasion? I'm thinking of the kind of validity check that was conducted in this study. If so, can you comment on what you know about your own error rates? And do you disclose and describe those error rates when you testify in a case?

DoubleLoop5 karma

  1. That's a difficult question to answers (which makes it a good one). There is no pre-set threshold that must be reached in order to reach an ID. This is because different features have different weights. A certain number of very discriminating features might be enough but the same number of very generic features wouldn't be. Additionally, distortion can effect the sufficiency threshold. All clear features might require fewer features while distorted and obscured features will require more to reach the same ID. Cedric Neumann's paper in the Royal Stat Society journal has a TON of data to back up these statements. So in the end, the decision is based on the training, experience, and expertise of the examiner (just like many other fields from botany to death investigation). The follow-up question is then, "How accurate are you at this decision?" Short answer - very.

  2. The bias issue is important but often overstated. In numerous studies testing the effects of bias on latent print examiners, there has not been a single case where bias led to an erroneous identification. Not saying that it's not possible, but it has never been documented during research.

As for the amount of info I have? That varies widely. I'm sometimes given the suspect's name, sometimes the victime's name. I'm usually given the item that the print came from or at least a description of it, but not always. I usually know the crime type, but not always. I usually don't know the details of what happened or how it happened, but sometimes I need to know whether an item belongs to the suspect (and his prints on it mean nothing) or if it belonged to the victim.

Glenn published a paper on this and found that it is extremely rare to find a high-profile case with highly biasing data where there is only a single ID. In other words, if there are multiple clear and obvious ID's, the amount of that data would tend to overpower any potential for bias.

  1. I am regularly tested, but not in that exact manner. That is something that I hope to work towards soon, but it's difficult to pull off. A lab system has multiple layers to prevent evdience from being "faked", even as a test. I do know of other labs working towards completing this kind of test. So results will be coming soon.

As to that specific article, there are some serious limitations to it. First, it was only 5 people, each doing one sample. Second, it only tested for erroneous EXCLUSIONS. Not a single examiner made an erroneous IDENTIFICATION in the study. From this, the field has recognized that there is a real danger of being biased into an exclusion and take steps to avoid making an error with that conclusion. However, it is extremely difficult to bias examiners into false IDs.

cuthman993 karma

Thank you for answering. I'll push my luck and ask for some follow-up:

Re: 1. You state,

"So in the end, the decision is based on the training, experience, and expertise of the examiner (just like many other fields from botany to death investigation). The follow-up question is then, 'How accurate are you at this decision?" Short answer - very.'"

Would it be fair, then, to conclude that you disagree with the National Academy of Sciences/National Research Council assertion that as a fundamental matter,

"All results for every forensic science method should indicate the uncertainty in the measurements that are made, and studies must be conducted that enable the estimation of those values,"

and that simply asserting that simply relying on a single examiner's 'experience and training' to give a decidedly qualitative description of certainty/error rates is unacceptable? Rather, in order to actually be considered a science (as opposed to, say, an art, or just an investigative technique developed and used exclusively by cops/prosecutors, not true science), it is necessary to, as they put it, "acknowledg[e] that there can be uncertainties in this process," and going forward "the concept of 'uniquely associated with' must be replaced with a probabilistic association"?

I guess the fundamental gist of this would be: the fingerprint analysis community has generally insisted that the work it does must by needs be subjective, i.e., rely on the 'training and experience' of a particular individual examiner to make many particularized judgement calls... whereas science, by definition, abhors that sort of subjectivity. The National Academies have strenuously urged that any reliance on a subjective system is always going to be flawed and un-scientific, and the analysts have pushed back against this, hard. Would you like to comment on that tension?

DoubleLoop3 karma

I would agree that that all MEASUREMENTS need to have an uncertainty of MEASUREMENT (or at least when it's close to the statutory limit; i.e. if someone has a metric ton of weed and they're only allowed to have an ounce, then a MOU isn't really necess). But fingerprint comparisons don't involve measurements. Not even sure how that could be done. I think that it would be more helpful (and understandable) to the courts to present accuracy data on the tests being performed.

But let me flip this back to you. How would an ME testify using MOU as to manner or cause of death? How would a psychologist testify to their opinions? A doctor? Are they then all labeled as unscientific?

I would disagree that the measure of scientificality is the use of probabilistics. Science is a much broader way of looking at the world then just stats.

There were some big changes that were made post-NAS. Many new studies have been published and the PCAST report even says many positive things about latent print comparisons.

The NAS Report was supposed to be a response to the forensic communities request for support from the feds. It's sad that it got turned into a way to undercut forensics.

RunDNA1 karma

There have been a number of recent high profile arrests (such as the Golden State Killer) using online DNA databases that can match DNA found at crime scenes to family members of the criminals, and then zeroing in on their identity.

What do you think of this new method? Is it as exciting and game-changing as it seems?

DoubleLoop3 karma


It'll probably even lead to some interesting Thanksgiving dinner discussions where someone asks if anyone has been submitting samples into GedMatch.

Everyone can help find the absolute worst criminals by getting their DNA profile and upload it. If you've got a distant relative that is a serial killer, case solved.

blahmkas1 karma

What are your thoughts on the Mayfield case regarding fingerprints not being as reliable as people actually think they are?

DoubleLoop3 karma

My opinion is that Mayfield is the best thing that ever happened to our field. It led to the best research to date regarding the accuracy of fingerprint examinations. The "Black Box" study shows that when fingerprint examiners say ID, they're right 99.8% of the time. Once verification by another examiner is applied, that basically goes up to virtually 100%.

The case defitintely raises questions for us by attorneys, but I think that it's appropriate and I'm thankful that I now have research to quote to respond to the challenge