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Cadaver dogs, how reliable are they at detecting death?

Author: admin | Files under Original Article

Originally written on 7th June 2008

Article by Dr Rosemary Claire Taylor MA MB BChir (Cantab)

Olfaction, the act or process of smelling, is the primary special sense possessed by dogs. A dog’s sense of smell is a thousand times more sensitive than humans. Dogs have more than 220 million olfactory receptors in their nose, whereas humans only have 5 million. Specially trained dogs have been used to locate forensic cadaver material and disaster survivors. Highly trained dogs assisted the emergency services in the aftermath of the terrorist attack on the World Trade Centre on September 11th, 2001.

Cadaver dogs need to undergo rigorous training. Prior to beginning a specialised training programme, these dogs need to have basic obedience skills. The cue a dog uses to indicate forensic material depends on the trainer. Some dogs are trained to bark to indicate cadavers, whereas others scratch at the area in the crime scene. Dogs are given a verbal cue to start searching, and directional cues such as “check it out” to indicate an area requiring a more detailed search.

A variety of breeds can be trained to hunt forensic material. Bloodhounds, springer spaniels and labradors are commonly used. Trained cadaver dogs have the ability to detect decomposing bodies beneath running water, for example when a corpse is weighted down, and placed at the bottom of a river.

I have done a thorough search of academic journals on this subject, and will present my findings as follows:

1. 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.

Carpet squares were used as an odor transporting media after they had been contaminated with the scent of two recently deceased bodies (bodies are all less than 3 hours old). 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).

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).

Cadaver dogs–a study on detection of contaminated carpet squares.
Oesterhelweg L, Kröber S, Rottmann K, Willhöft J, Braun C, Thies N, Püschel K, Silkenath J, Gehl A.
Institute of Legal Medicine, University Medical Center Hamburg, Germany.

Notes on the scientific terminology in this study;

Sensitivity means the number of correct detections out of 100. Here, all dogs managed to correctly identify 75-100 carpet squares out of 100. This is a good success rate.

Specificity describes the number of false identifications. A sensitivity of 91 out of 100 means, at most, there are 9 false positives in a sample of 100 uncontaminated squares. This is a good specificity, much higher than cervical screening, which can detect far more false positives.

The Positive Predictive Value can be defined as;

In other words, out of 100, there are 75-100 true positives, and 0-9 false positives. A positive predictive value describes the percentage chance, if a sample is contaminated, that the dog will discover it. The value of 90-100 means that, out of 100 contaminated squares, at least 90 are correctly identified by the dog.

The Negative Predictive Value can be defined as;

In other words, out of 100, there are 0-9 false positives and 0-25 false negatives. A negative predictive value describes the chance that, if a sample is not contaminated, the dog will correctly identify the sample as clear of human remains. The study quotes a negative predictive value of 90-100. This means only 0-10 ‘clean’ squares are wrongly identified as contaminated by the dogs.

Accuracy is the degree to which the evidence presented by the dogs matches known information about which squares were marked. The accuracy of dog detection is presented as 92-100. This means that dogs correctly identify carpet squares as ‘marked’ or ‘unmarked’ in at least 92 cases out of 100. This is an impressive accuracy score.

In addition, I think it is important to consider that this is an experiment, not real life. In reality cadaver dogs are given more time to assess possible traces of human remains. Hence in a true police setting, cadaver dogs are more likely to give accurate information.

2. Specially trained air scent detection canines (Canis familiaris) are commonly used by law enforcement to detect narcotics, explosives or contraband, and by fire investigators to detect the presence of accelerants. Dogs are also used by police, military, and civilian groups to locate lost or missing persons, as well as victims of natural or mass disasters. A further subspecialty is “cadaver” searching, or the use of canines to locate buried or concealed human remains.

Recent forensic investigations in central Alberta demonstrated that the use of cadaver dogs could be expanded to include locating partial, scattered human remains dispersed by repeated animal scavenging. Eight dog-and-handler teams participated in a two-month training program using human and animal remains in various stages of decay as scent sources. Ten blind field tests were then conducted which simulated actual search conditions. Recovery rates ranged between 57% and 100%, indicating that properly trained cadaver dogs can make significant contributions in the location and recovery of scattered human remains.

J Forensic Sci. 1999 Mar;44(2):405-8.
The use of cadaver dogs in locating scattered, scavenged human remains: preliminary field test results. Komar D.
Department of Anthropology, University of Alberta, Edmonton, Canada.

This study was written in 1999. Nonetheless, in situations where there are scattered human remains, dogs identify them in 57-100% of cases.

3. 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 skeletonised. 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 skeletonised remains buried at a significant depth. Fresh and skeletonised 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.

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 AE, Jacobi KP, Farley R, Hensel L.
Department of Anthropology, University of Alabama, Tuscaloosa, AL 35487-0210, USA.

This is an impressive study. The salient points are that cadaver dogs can identify a corpse, or a piece of a corpse, which had been buried at a significant depth. This gives the dog handlers an opportunity to investigate a more ‘real life’ crime scene. Following a murder, it is normal for a criminal to hide any human remains, often by burying the corpse. It appears that these dogs can still detect the ‘smell of death’, when a body part is buried deep in a forest.

The Eugene Zapata Case

Eugene Zapata’s wife, Jeanette Zapata was last seen on October 11th, 1976. Her body was never found. Police suspected that her husband had murdered her, but without sufficient evidence to arrest him, her disappearance became a cold case. It was reopened due to pressure from Mrs Zapata’s loved ones, and cadaver dogs were used to locate her remains. The link for this article is

Jeanette “Jean” Zapata sent her two teenage daughters and 6-year-old son to school shortly after 8 a.m. Oct. 11, 1976. They last saw her as she sat at the kitchen table in their East Side home near La Follette High School wearing blue corduroys and a striped top.

The 36-year-old flight instructor – who was divorcing her husband – was never heard from again.
Madison Police Capt. Tom Snyder said Thursday that the husband, Eugene J. Zapata, is their primary and only suspect. He lives in Nevada with his second wife.

According to a search warrant executed by police in August but kept sealed until Thursday morning, dogs trained to detect human remains reacted to two locations connected to Eugene Zapata – a crawl space in the couple’s former home and a storage locker in Sun Prairie.

Two days after Jeanette Zapata’s children saw her for the last time, Ivan Norton, an accountant at Frickleton School of Aeronautics, reported her missing because she hadn’t come to work.

“If she told you to make an appointment at a certain time, she was there ahead of schedule to make sure it all went right,” Norton, 69, said Thursday. “She was very nice and very prompt and that was the whole thing that was concerning us. She was like a time clock.”

Immediately after she disappeared, her purse and other belongings, including her new car, were found at the home, but a .30-06 rifle was missing.

Investigators said in the search warrant:

Officers have questioned Eugene Zapata several times over the past 30 years and he sometimes provided contradictory statements.

Zapata told police he argued with his wife over visitation rights to their children a few days before she disappeared. The day she vanished, they met with the La Follette High School principal to discuss their oldest daughter. One time he told police he called the morning of Oct. 11 to cancel the meeting. On another occasion, he said he went to the house at 9 a.m. to pick her up.

Jean Zapata had obtained a court order that restricted his time with the children in the home to two hours on Saturday mornings.

His employment records at the state Department of Transportation indicate he worked from 7:45 to 8:45 a.m. the day she disappeared, was off work the following day, Oct. 12, and then came in to work at 12:30 p.m. Oct. 13.

He told police he took Oct. 12 off to care for his children at home, but investigators verified the children were at school.

Zapata did not respond to messages from the State Journal asking for an interview. In a 1987 State Journal article, he said he believed his former wife ran away.

“It may have been just the pressure of it because I filed for custody of the kids,” Zapata said then. “She was a very strong-willed person. If she made up her mind that she wanted to disappear, she could do it.”

Investigators suspected Zapata, but lacking leads they had shelved the case.

It was reactivated a year ago after one of Jean Zapata’s childhood friends called asking about its status, Snyder said.

New detection techniques, including “cadaver dogs” that can find faint odors of human remains, pushed the investigation forward.

According to court documents, dogs twice signaled that they had found the scent of human remains in an unused basement crawl space at the Zapatas’ former home on Indian Trace, and a human hair was excavated. Police will not say whether test results indicate that it belonged to Jean Zapata.

Eugene Zapata sold the house in 1997. In 2001, he moved to Nevada. He rented a storage facility in Sun Prairie that year and listed its contents as “boxes, mixture of son’s and parent’s stuff.”
According to the search warrant:

On April 13, 2005, police left a message for Eugene Zapata with his wife in Nevada. The next day, the locker’s key was returned to U-Store Mini Storage in Sun Prairie. The empty locker remained locked until Aug. 10 and 11 when police opened it.

Dogs detected the scent of decomposing or decomposed human remains inside and around the locker, the search warrant indicates. That prompted a search of four acres in rural Juneau County owned by Zapata since 1978.

Nothing was found on the land, which was for sale.

Snyder stopped short Thursday of saying he believes Jean Zapata was murdered by her husband and could not predict if an arrest was imminent.

But he did say he believes she met with foul play and her husband is the only suspect.

The McCanns’ lawyers used the Zapata case to indicate an example of how a seemingly innocent man, can be incriminated by the cadaver dog evidence.

Madeleine: McCanns consult American lawyers over ‘cadaver dog’ evidence

Daily Mail Last updated at 18:07 16 September 2007 (Link to original article here)

Kate and Gerry McCann’s legal team have consulted the lawyers of an American man accused of murdering his estranged wife in a case where cadaver dog evidence was key, a source said today.

Two British sniffer dogs, one capable of detecting blood and human remains, were brought to Portugal in early August.

The cadaver dog picked up a “scent of death” on everything from Mrs McCann’s clothes to missing Madeleine’s favourite soft toy Cuddle Cat, according to reports.

During police interviews the McCanns were shown a video of the animal “going crazy” when it approached their Renault Scenic hire car, newspapers have claimed.

Leaked reports from the investigation have suggested Madeleine’s parents could have accidentally killed her and then disposed of her body using the car.

Although they do not know the full details of Portuguese prosecutors’ case against them, the McCanns are concerned it may rest on the dog’s reaction.

They want to highlight the judge’s dismissal of cadaver dog evidence in the high-profile Eugene Zapata murder trial in Madison, Wisconsin.

The couple’s lawyers have already contacted Zapata’s defence team, who are now sending their large file on the matter to Britain.

Zapata’s estranged wife, flight instructor Jeanette Zapata, was 37 when she vanished on October 11 1976 after seeing her three children off to school. Her body has never been found.

Detectives suspected Zapata of involvement in her disappearance but did not charge him because of a lack of evidence.

Police decided to conduct new searches using cadaver dogs, a new investigative technique, when an old friend of Mrs Zapata contacted them about the case in 2004.

Zapata, 68, was charged with first-degree murder last year after the dogs indicated they sniffed human remains in a small basement “crawl space” at the former family home in Madison and other properties linked to him.

But Dane County Judge Patrick Fiedler ruled last month that the evidence that led to the charge could not be put before the jury.

He said the dogs were too unreliable in detecting the odour of remains and noted that no remains were actually found.

The judge agreed with an analysis of the three dogs’ track record by Zapata’s defence team that found they were incorrect 78 per cent, 71 per cent and 62 per cent of the time.

According to the Wisconsin State Journal, Mr Fiedler told the court: “The state has failed to convince me that it’s any more reliable than the flip of a coin.” Zapata denies murder, and the jury in the case went out on Friday to start considering its verdict.

A source close to the McCanns’ solicitors said: “The legal team are in touch with the lawyers who represented the defendant in the case.

“The court papers, giving the legal submissions, are on their way to the McCann team for consideration.

“At the moment there are no formal charges and therefore there is no formal allegation against which the McCann team can work. We are having to work a little bit in the dark.

“But given that we understand the central plank of what the police are alleging involves sniffer dogs – albeit British ones which are said to be particularly good – this is important and relevant, and will be raised with the police and brought to the judge’s attention.”

Unfortunately for Kate and Gerry, Mr Zapata eventually plead guilty to his wife’s murder on February 19th, 2008.

Zapata Enters Guilty Plea In Connection With Missing Wife’s Death

Former Madison Resident Plead To Reduced Charge of Homicide By Reckless Conduct
(Link to original article here)

UPDATED: 7:18 am CST February 19, 2008 MADISON, Wis. — Eugene Zapata entered a guilty plea on Monday to a reduced charge of homicide by reckless conduct in connection to his wife’s disappearance 30 years ago and was sentenced to time behind bars.

Appearing in Dane County Circuit Court on Monday, Zapata was sentenced to five years in prison after entering the guilty plea. Zapata, 69, pleaded guilty as part of a deal with prosecutors. The sentence was the maximum sentence for the charge, WISC-TV reported

Old sentencing rules likely mean that Zapata will spend just more than three years in prison, but the judge and prosecutors supported the deal, saying that it would give family and friends closure and let them heal, WISC-TV reported.

Dane County Judge Patrick Fiedler, who sentenced Zapata, said that the important thing is everyone now knows what happened to Zapata’s wife, Jeanette. Dane County District Attorney Brian Blanchard said that the plea deal gives closure to Jeanette Zapata’s loved ones.

“Part of what happened after Madison police took over a cold case from nowhere to today is the ability now to have the family and friends of Jeanette Zapata know exactly what happened to her.”

Eugene Zapata was to have faced a second trial late next month. A former Madison resident, he was tried last year for the disappearance and presumed death of his wife in 1976. Her body was never found.

He had faced first-degree murder charges. A jury deadlocked on a verdict, and a second trial was scheduled. If convicted on that charge, Zapata would have faced life in prison.

A second trial seemed less likely after reports surfaced earlier this month that a plea deal had been struck.
As part of the agreement with prosecutors, Zapata had to tell authorities how he killed his wife and where her body was hidden, WISC-TV reported.

During Monday’s proceedings, Dane County chief prosecutor Bob Kaiser asked the court to accept an amended charge of homicide by reckless conduct. Kaiser earlier told the court that the deal with Zapata includes a statement to police about why Zapata went to her house, how and why he killed her and what he did with her.

Kaiser said that Zapata confessed to police and that he believes Zapata’s statement will be truthful and complete.

Prosecutors said that Zapata told police that he went to his wife’s house in 1976, had an argument and “snapped.” He told them that he grabbed a metal draftman’s tool and hit her in the head multiple times. He said that she then dropped to ground and he strangled her. He apparently told investigators that he “strangled Jeanette Zapata manually until his hands hurt.” He also wrapped a cord around her neck.

Zapata said that he wrapped her body in a tent and drove it to an area near Highway 151 and Reiner Road, where he hid it in some underbrush. He transferred her remains a short time later to some Juneau County land that he owed. There, he buried her body — which remained there for 24 years — before moving her remains to a Sun Prairie storage locker, where it was eventually cut into pieces and later disposed of at a Mauston landfill. He moved the body from the Juneau County because he planned to sell the land.

Linda Zapata, the youngest of Eugene and Jeanette Zapata’s three children, gave a statement in court. She said that she was torn over testifying against her father earlier, but she’s glad that he agreed to the plea deal. She said his confession is “a gift.”

“By confessing to Mom’s murder, you have given me and others a precious gift, a chance to grieve, mourn and heal,” she said. “Mom deserved no less than that Mom deserved the truth about what really happened that morning, and I thank you for finally giving her that.”

She added that she still loves her father and forgives him, although she doesn’t condone what he did.

Blanchard said because Jeanette Zapata’s body was dumped in numerous Dumpsters at the landfill, there is no way to recover her remains.

Eugene Zapata declined comment in the court. He was later taken away in handcuffs after his sentence was imposed.

Kaiser said that he thinks the agreement is the best possible option for “truth and justice.” Likewise, Blanchard called the resolution to this case a huge achievement for justice.

Mrs McCann attends the death of six of her patients, prior to her holiday

Extract from Scapegoats? McCanns reject ‘compelling’ new police evidence

Belfast Telegraph 10th September 2007

Forensic experts have also warned that evidence obtained from the use of cadaver-smelling dogs is open to challenge. According to the McCann family, detectives asked why a British-trained dog detected traces of a corpse on Mrs McCann’s clothing and on a Bible in the apartment. Mrs McCann, a GP, has said she was present at six deaths before her holiday. Despite it being said that dogs’ noses are anywhere between 1,000 and 10,000 times more effective than humans’, and despite the dogs’ training to detect traces of everything from drugs to cancers, experts warn that there are still difficulties using evidence uncovered by dogs.

I have worked as a junior doctor in general practice, and my sister is a GP. Doctors are called to certify death on occasions. Typically the patient is an elderly person in a residential or nursing home. Thankfully this does not occur very often. A doctor has to check for a heartbeat, respiration, and whether the pupils react when a pen torch is shone into the eyes. I find the claim that Mrs McCann attended six deaths, shortly before the her holiday, difficult to believe. People tend to die on hospital wards, and when a patient in a care home becomes unwell, they tend to get admitted to a hospital. Why the scent of death was on Mrs McCann’s Bible also raises suspicions. Are we supposed to believe she took this Bible with her when she was at work? Was she reading her unfortunate patients their Last Rites? Unbelievable.

11 responses. Wanna say something?

  1. Jakbop
    May 15, 2009 at 01:46:33

    Obvious question: Was this story about attending six deaths checked by police?

  2. Sasha
    May 24, 2009 at 16:03:04

    A very informative article 🙂

    I wonder if you’d be able to help me put an argument to rest which crops up from time to time in my household.

    Is it possible for Eddie and Keela to give a positive reaction to synthetic cadaver odour that’s generally used by other trainers with their dogs?

    I’m new to the McCann case and just beginning to understand what is what but I don’t have enough experience with blood and cadaver dogs to say one way or the other.

  3. SMK
    Jun 1, 2009 at 18:19:51

    It is unbelievable to me that this forensic evidence would be compiled and not lead to an arrest, or re-opening of the case. Something very amiss here, and I agree with the poster above: Where is the evidence of her having attended 6 deaths?

  4. lairdtc
    Jan 14, 2010 at 21:00:30

    GP s very rarley come into contact with corpses and they dont wear there holiday clothes to work DOH

  5. mccanns should be in jail
    Oct 6, 2010 at 12:40:42

    why havent they beeen charged at what point do the police say – shes dead and the proof is there – cadavar dogs – DNA – inconsistencies in the timeline – 3 paaaports in the room when photographed the physical impossibilities of taking a sleeping child out of the window – madeline made a ward of the state lesss than a fortnight after sjhe disappeared – – the mccanns should be in jail

  6. And
    Dec 23, 2010 at 21:18:16

    Well the dogs were right after all in the Zapata’s case. So the Mccans can not use this again. How many people thought that the dogs were not totally accurate and then were proved wrong as the confession states clearly what Zapata had done to the body and where he had put the remains! What a coincidence the exact places the dogs pointed out!!
    The dogs don’t lie…

  7. Marc
    Apr 29, 2011 at 13:17:46

    Condisdering that a dog’s sense of smell is 200,000 times more acute than a human’s, the entire notion of a false positive is so absurd as to be nonsensical.

  8. Shaun
    Aug 28, 2014 at 17:38:45

    Even if you believe her claim about the deaths before the holiday, did they occur in the cupboard in the apartment or the car, or behind the sofa? And why did the dogs, which have a 200 from 200 success rate by the way, or did at the time, not find evidence on all her clothing? why just the jazzy jogging pant/pajama bottoms she must wear to her scarily high number(almost Harold Shipman esque) of patient deaths/funerals

  9. Peter
    Nov 2, 2015 at 00:44:20

    A second pair of cadaver dogs should have been introduced to the scene, trained elsewhere and with a different handler.
    On the rare chance that a false positive signal was given by one dog, it would have been quite compelling if the same areas were alerted by another.

2 Trackback(s)

  1. May 12, 2011: Is it true Madeleine Mccan's mum has released a book?
  2. Oct 23, 2011: Cadaver Dogs and Missing Baby Lisa and now the Stranger Carrying a Naked Baby – what to believe. « Linda's Tracking Hounds

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