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Strongest evidence comes from British forensic dogs Mm11

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Strongest evidence comes from British forensic dogs

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Strongest evidence comes from British forensic dogs Empty Strongest evidence comes from British forensic dogs

Post by PLL on 25.08.18 13:55

Even if a layman, I'll try to demonstrate in my humble opinion that the strongest evidence found so far comes from British sniffer dogs, especially from the cadaver dog, and that a lot of emphasis has been placed on DNA evidence, but this is meaningless.

Eddie, the cadaver dog (EVRD) spotted a cadaver in some locations in McCann’s apartment. This is strong evidence that there's been a cadaver there, but the dog can't tell who's the cadaver, only that it was a human cadaver based on its training.

After throughout search, there's no evidence there's ever been a known cadaver within the apartment, so it's more than reasonable to think that it might only be Madeleine's, the girl who disappeared. The ultimate evidence would be finding the cadaver. Let's suppose there was a disaster and you're searching for dead people. The dog spots a place. This is strong indication there's a cadaver there. After you dig in wreckage, you find the cadaver and this is ultimate evidence. Once the dog is highly reliable, it's more than wise to dig in priority the places spotted by the dog and not elsewhere.

A. = EVIDENCE FROM EDDIE, THE CADAVER DOG (EVDR):

From https://jillhavern.forumotion.net/t15221-sniffer-dogs-the-campaign-against-eddie-and-keela-and-vanity-fair-story-about-maddie

1. "[...] a judge ruled last month that the evidence was no more reliable than ‘the flip of a coin’ and could not be put before a jury”.

2. "[Gerry McCann] mentioned [...] that “the fragility of these dogs has been proven in a study conducted in the USA, about a man accused of murder. They had ten rooms, and in each they placed four boxes with vegetables, bones, trash. Some had human remains. They stayed there ten hours. Eight hours after they took the boxes out came the dogs. And the dogs missed two-thirds of the attempts. Imagine reliability when these dogs test an apartment three months after a child disappears”, he concluded".

Statements 1 and 2 disclose both judge and Gerry are ignorant about scientific reasoning. In either case, spotting only 50% of human remains, like a tossed coin, or just 1/3 of the cases as claimed by Gerry makes theses dogs highly reliable, as we'll see.

Let's use a medical qualitative test as an example. These tests tell a result is either positive or negative only, not how much positive or negative, unlike a quantitative test. A quantitative test might be for instance a glicemic index (for diabetes), say a glicaemia of 181mg/dL (sugar in blood). A qualitative test might be a rapid HIV strip test, which only gives either a positive or negative result, no numbers.

In a medical qualitative test, in which you have either a positive or a negative result, you must interpret it by using a priori probabilities calculated by manufacturer and researchers on known samples.

Either result, positive or negative, can be false or true. You call specificity to the probability a negative result is true and sensibility the probability a positive result is true.

If you have a 100 known negative samples (tested by a certified method, called gold standard) and your test gives 90 negative and 10 positive results, the you have a 90% specificity, that is the probability a negative result is true is 90%, so this is its specificity.

Then you test 100 certified positive samples, and your test gives 95 positive and 5 negative results. Now, your probability that a positive result is true is 95%, so the sensibility is 95%.

So, we use negative samples only to calculate specificity, and positive samples only to calculate sensibility.

==============> You may wish to read the note (1) below, which is not critical for discussion.

So, if your result is positive, it's either a false positive (probability 10%, you use specificity here from challenging the test against certified negative samples) or a true positive (probability 95%, you use sensibility here from challenging the test against certified positive samples). If it's negative, it's either a false negative (probability 5%, using sensibility) or a true negative (probability 90%, using specificity).

Now let's return to the judge and Gerry and think accordingly. Let's discard judge, once he gives a more abstract example, even if equivalent to Gerry's, as we’ll eventually see.

Gerry claims the dogs missed 2/3 of samples containing human remains. This seems impressive and likely makes one think the dogs are unreliable. They're only demagogically unreliable. If fact, they're highly reliable.

We don't know exactly how many samples were there in Gerry's example, but let's suppose there were 100 true negative samples (no human remains) and 100 positive samples (human remains) for the sake of simplicity.

So, Gerry claims the dogs missed 2/3 of samples containing human remains, that is they only detected 1/3 of positive samples and none of those samples (detected by dogs) were negative (no human remains). Now let's judge this scientifically:

- The dogs had 100 positive samples and 100 negative samples. They spotted 33 samples and discarded 167 samples.

- Only 100 of 167 discarded samples are true negatives, so we use specificity here, and we have 100/167, or 60% (probability a discarded sample is negative indeed).

- All 33 spoted samples are true positives, so we use sensibility here, and we have 33/33, or 100%!!!!!!

Concluding: You can trust positive results, they're 100% reliable, but not negative results, only 60% of these are reliable.

The same applies to the judge, except that he claims the dogs spot 50% of true positives, not just 33%, like Gerry claims.

So, what does Gerry mean? He means the dogs are unreliable in that they may have missed other places where there was a cadaver, but they're highly reliable in that the places they spotted a cadaver are but true positives.

After it was excluded that any known cadaver has ever been in McCann's apartment, the only reasonable judgement is that it might only belong to Maddie, the missing girl. Once a cadaver has never been found, Gerry is right for our frustration in that there's no ultimate forensic evidence. Anyway that's a strong indication ("indício in Portuguese) that the girl died, and so it's useless to focus investigation on abduction, and most means should be poised to a death (deliberate or not).

I don't know what Gerry is talking about (if anyone knows), but probabily the judge only reject dog's evidence because that lacked ultimate forensic evidence, that is no cadaver found.

==============> (1) As a parenthesis only, in real life you don't have gold standards, only unknown samples. You have real people samples and must make decisions from results. Here, your probability (called predictive probability) depends on composition of your sample. But, how do you know which true results you have in your population? You can't but guess: if you have a drug addict and you're testing them for a rapid HIV test, which is positive, then your predicitve probability is very high it's a true positive. If you're deciding a positive result in a blood donor, your predictive probability is very high it's a false positive. So you'll take almost for granted that a positive result is true in a drug addict and false in a blood donor (please note that these are mere hypothetical examples as supplementary tests would be done anyway and testing blood donors for using their blood is not that simple).

B. = EVIDENCE FROM KEELA, THE BLOOD DOG (CSI):

Again from https://jillhavern.forumotion.net/t15221-sniffer-dogs-the-campaign-against-eddie-and-keela-and-vanity-fair-story-about-maddie

1. "Gerry McCann, on the sole interview he gave to a Portuguese newspaper, the weekly “Expresso”, was also very aggressive towards the capacity of the “wonder dogs”. Answering a question about what the the fact the the dogs found “traces of blood in the apartment and in the car”, he claimed that “no blood was found” and said “the evidence is worthless without being corroborated by forensic information. And they were not”.

A lot of emphasis has been placed on DNA analysis of samples from locations spotted by Keela, the blood dog (CSI), and a lot of frustration on the lack of ultimate results by the Forensic Science Service (FSS).

I think scientists from FSS are honest people, and they offered the best results they could. As they mention in their report, and this is the hardest part to understand, any low copy number (LCN) DNA testing alone is very cumbersome in that it can't tell how DNA was deposited, which fluid it comes from, and if any crime was committed.

People rely a lot in DNA analysis for its sophistication and uniqueness of DNA, but FSS scientists are right in being a lot cautions, as they can't grant what they're talking about.

This is a lot different from sampling a blood spot in a wall and test it for DNA. Here we know what we're talking about. But when you use LCN, you're using invisible samples, and this is the greatest problem.

LCN won't grant you're testing blood, or whatever sample you can imagine, only that DNA is found. And finding Maddie's DNA in an apartment where she spent holidays might not be big deal.

Here we have an example of catastrophic DNA analysis from Scientific American (June, 2016):

In December 2012 a homeless man named Lukis Anderson was charged with the murder of Raveesh Kumra, a Silicon Valley multimillionaire, based on DNA evidence. The charge carried a possible death sentence. But Anderson was not guilty. He had a rock-solid alibi: drunk and nearly comatose, Anderson had been hospitalized — and under constant medical supervision — the night of the murder in November. Later his legal team learned his DNA made its way to the crime scene by way of the paramedics who had arrived at Kumra's residence. They had treated Anderson earlier on the same day — inadvertently “planting” the evidence at the crime scene more than three hours later. The case, presented in February at the annual American Academy of Forensic Sciences meeting in Las Vegas, provides one of the few definitive examples of a DNA transfer implicating an innocent person and illustrates a growing opinion that the criminal justice system's reliance on DNA evidence, often treated as infallible, actually carries significant risks.

As you can see, unknowing how to link a DNA analysis to a concrete sample, it's too risky to use its result forensically. That's why FSS scientist's report is so cautious and frustrating.

C. = CONCLUSIONS:

Solid evidence (if only at an indication level) here is Eddie's spotting of cadaver scent in McCann's apartment, and also Keela's spotting of blood in those locations. It's meaningless that so many months had passed, as dogs are trained to detect scents at molecular levels and anyway their spottings are unlikely to result from chance alone or from suggestion. Results in car are harder to interpret, but again far from random. Anyway, at least for cadaver scent I think "plantation" couldn't be excluded.

Now we must poise investigation to a death, and find ultimate forensic evidence. Perhaps a good starting thread would be trying to trace any possible scenarios to made it possible to make a cadaver disappear in an unknown holiday place in such a small lapse of time.
PLL
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Strongest evidence comes from British forensic dogs Empty Re: Strongest evidence comes from British forensic dogs

Post by PLL on 31.08.18 23:50

Here we have some interesting found articles about cadaver dogs.

We have dogs that can detect cadaver odour 667 days after corpse was removed from a surface outdoors.

Also dogs that detect cadaver odour in carpets that were close to cadavers (not touching) for 2 and 10 minutes, over 35 and 65 days, respectively.

Even dogs that can locate skeletonized remains buried at a significant depth. An important caveat here, authors understood that dog handlers affected their reliability.

Yet, Professor Gerry P. McCann refutes scientific evidence used in investigation of his daughter with demagogic disdain.

Forensic Sci Int. 2015 Apr;249:304-13.

Application of soil in forensic science: residual odour and HRD dogs.

Alexander MB1, Hodges TK2, Bytheway J3, Aitkenhead-Peterson JA4.

Abstract

Decomposing human remains alter the environment through deposition of various compounds comprised of a variety of chemical constituents. Human remains detection (HRD) dogs are trained to indicate the odor of human remains. Residual odor from previously decomposing human remains may remain in the soil and on surfaces long after the remains are gone. This study examined the ability of eight nationally certified HRD dogs (four dual purpose and four single purpose) to detect human remains odor in soil from under decomposing human remains as well as soils which no longer contained human remains, soils which had been cold water extracted and even the extraction fluid itself. The HRD dogs were able to detect the odor of human remains successfully above the level of chance for each soil ranging between 75% and 100% accurate up to 667 days post body removal from soil surface. No significant performance accuracy was found between the dual and single purpose dogs. This finding indicates that even though there may not be anything visually observable to the human eye, residual odor of human remains in soil can be very recalcitrant and therefore detectible by properly trained and credentialed HRD dogs. Further research is warranted to determine the parameters of the HRD dogs capabilities and in determining exactly what they are smelling.


Forensic Sci Int. 2008 Jan 15;174(1):35-9

Cadaver dogs--a study on detection of contaminated carpet squares.


Oesterhelweg L1, Kröber S, Rottmann K, Willhöft J, Braun C, Thies N, Püschel K, Silkenath J, Gehl A.

Abstract

INTRODUCTION:

Cadaver dogs are known as valuable forensic tools in crime scene investigations. Scientific research attempting to verify their value is largely lacking, specifically for scents associated with the early postmortem interval. The aim of our investigation was the comparative evaluation of the reliability, accuracy, and specificity of three cadaver dogs belonging to the Hamburg State Police in the detection of scents during the early postmortem interval.

MATERIAL AND METHODS:

Carpet squares were used as an odor transporting media after they had been contaminated with the scent of two recently deceased bodies (PMI<3h). The contamination occurred for 2 min as well as 10 min without any direct contact between the carpet and the corpse. Comparative searches by the dogs were performed over a time period of 65 days (10 min contamination) and 35 days (2 min contamination).

RESULTS:

The results of this study indicate that the well-trained cadaver dog is an outstanding tool for crime scene investigation displaying excellent sensitivity (75-100), specificity (91-100), and having a positive predictive value (90-100), negative predictive value (90-100) as well as accuracy (92-100).



J Forensic Sci. 2003 May;48(3):617-21.

Cadaver dog and handler team capabilities in the recovery of buried human remains in the southeastern United States.

Lasseter AE1, Jacobi KP, Farley R, Hensel L.

Abstract

The detection of human remains that have been deliberately buried to escape detection is a problem for law enforcement. Sometimes the cadaver dog and handler teams are successful, while other times law enforcement and cadaver dog teams are frustrated in their search. Five field trials tested the ability of four cadaver dog and handler teams to detect buried human remains. Human and animal remains were buried in various forested areas during the summer months near Tuscaloosa, Alabama. The remains ranged in decomposition from fresh to skeletonized. Cadaver dogs detected with varying success: buried human remains at different stages of decomposition, buried human remains at different depths, and buried decomposed human and animal remains. The results from these trials showed that some cadaver dogs were able to locate skeletonized remains buried at a significant depth. Fresh and skeletonized remains were found equally by the cadaver dogs along with some caveats. Dog handlers affected the reliability of the cadaver dog results. Observations and videotape of the cadaver dogs during field trials showed that they were reliable in finding buried human remains.
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