Septic Tank Evidence

by Laura James

Unfortunately, septic tanks sometimes end up holding more than household sewage. Occasionally they have been known to yield the bodies of women who have been murdered, usually by very foolish men who think that nobody will ever think to look in the septic tank. Sometimes it might take a while, but eventually, both septic and murder will out.

Recently I learned that a more mundane sort of evidence can be found in septic tanks, placed there by those making the same foolish mistake of thinking that a septic tank is a good place to hide evidence.

I had my septic tank pumped out recently. The fellow who did this nasty business for me regaled me with a curious story.

Larry explained that he had been the "star witness" in a few divorce cases. I wondered where he was going with this. This was a surprising thing to say, as Larry fit the image of a man who spent all day with septic tanks, not a star divorce witness. He wore a University of Missouri T-shirt. I had asked him if he was from Missouri, as I've been spending a lot of time there lately. "It's just a shirt," he said sheepishly. He proceeded to tell me how he's come to be subpoenaed for the third time to testify.

Women, it seems, flush things down the toilet that they shouldn't, besides tampons. (Flushed tampons cause no end of trouble to public sewer systems everywhere, because the strings never dissolve and they get entangled in tree roots, causing massive plumbing blockages.) There's something else that shouldn't be flushed -- into a septic tank anyway -- and that's a used condom, particularly one that is being flushed by a woman whose husband has had a vasectomy.

Larry the septic tank hauler has had to testify three times now that condoms, when flushed down a toilet and into a septic tank, will float on top until someone like Larry pries off the lid and reveals more than the usual septic tank contents.

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Trace: It's the Little Things

by Andrea Campbell

Remember Locard's Exchange Principle, that whenever two objects come into contact a transfer of material will occur? Trace evidence—fibers, fabric, pet hair, paint chips and a thousand other items and artifacts can help to place the accused at a crime scene. While matching a tiny piece of evidence with its source may not be enough to link a suspect to a crime, when the pieces start to pile up it becomes more than coincidental and begins to become “conclusive” evidence. The more relevant the fibers found, the more convincing the evidence.

It is natural then, that fabrics, which are millions of fibers woven together, may provide the most compelling evidence of all. Fabric matches are much like jig-saw puzzles, the pieces must be found and reconstructed with exactness and certitude.

Hair and fiber evidence is useful in:

1. Helping to establish the scope of the crime scene
2. Placing a perpetrator at a scene
3. Connecting a suspect with a weapon
4. Supporting witness statements
5. Connecting crime scene areas (abduction, vehicle used, dump site)

Sources of Fibers

Fibers are divided into classes. There are four major types: animal fibers such as wool, vegetable fibers like cotton, asbestos is the only mineral fiber, and manmade or synthetic fibers such as polyester. Synthetic fibers make up about 75 percent of all textile fibers—there are over 1,000 different types in the United States and, consequently, they are the most common fiber investigated in the crime lab.

Tiny Details

As with other types of evidence, trace evidence is kept separate in a file or box, documented with the date and time, the name of person collecting it, a description, a case number for filing, and a sketch or photograph of where it came from. The chain of custody—a list of every person who touched it—is maintained for each item, no matter how small. Since evidence in this category can be wee stuff, preventing contamination and loss is a must, and trace evidence is usually collected before other examinations.

Finding the objects begins with a general look-see, but different types of alternate light sources such as UV, laser, and high intensity lamps may be needed.

The Little Things

A single thread is a fiber made up of tiny filaments. When fibers rub together, they leave fragments of themselves on each other and everything around it. As evidence, we could call hairs and fibers evidentiary minutiae because some particles can best be seen through a microscope.

Where Fibers are Found

Hairs and fibers can be found in the most remarkable of places but generally come from clothing, drapery, wigs, carpeting, furniture and blankets. Because fibers are transferred in such large numbers, they are much more likely to be found at a crime scene and are more likely to have a common origin. For example, a wool thread caught on a window sill at a crime scene could be matched to a pulled thread on the sweater found at the suspect’s house. However, it is actually quite common to find them in the barrel of guns! They get in there through a phenomenon called "blowback". The blast of a gun produces a vacuum in the wake of a wave of high-velocity gases. This negative phase creates a vacuum, which sucks up things in close proximity such as hair or fibers.

In 1982, a girl named Kristen Lea Harrison was abducted from a ball field in Ohio and her body was found six days later thirty miles away. She had been raped and strangled. Investigators found orange fibers in her hair that looked similar to those found on a twelve-year old murder victim eight months earlier in the same county. Some time later, a 28-year old woman was abducted and held prisoner in a man’s home. He tortured her and she was afraid for her life. After he left, she escaped and reported him. Police found a van with orange carpeting and scientists traced it back to Robert Anthony Buell. Other evidence helped to establish a more solid link and Buell was eventually convicted.

Fiber and Hair Collection

Fibers are collected in several different ways.

Picking. If visible to the eye, items can be picked up with tweezers or a section can be cut out and put into paper packets or petri dishes.

Lifting. Sometimes trace evidence is collected by taking wide cellophane tape and rolling it over the suspected area. The collected lifts are typically placed on a transparent backing such as clear plastic sheeting, easy for viewing under a microscope.

Vacuuming. Often, car seats, floorboards, and trunk space are vacuumed for fiber particles when there is a suspected abduction or when probable cause indicates the transportation of a murder victim or some illegal product. (*Note: some jurisdictions no longer use a vacuum.)

Scraping. Trace evidence scraped from clothing onto clean paper with a spatula or similar tool is used to dislodge certain items. This technique is most often conducted within the laboratory in a controlled environment that reduces the risk of contamination.

Combing. A clean comb or brush is used to recover trace evidence from the hair of an individual. The combing device and collected debris from the hair should be packaged together.

Clipping. Trace evidence can be recovered from fingernails by nail clipping, scraping or both.
Commonly, fingernails from the right and left hands are packaged separately.

Pieces of fabric found at the scene can be examined in a manner similar to fibers to determine color, type of cloth and fiber, thread count, direction of fiber twist and dye. When fabrics are torn or cut apart, the ends can be matched physically to another piece. In hit-and-run cases, pieces of the victim’s clothing are often found on the grill, the car’s fender or door handle.

Analysis of Fibers

Experienced examiners must have a good eye for comparison. At times they look at literally hundreds to thousands of hairs and fibers under a comparison microscope and from these weed out the few matches. Special microscopes found in some labs can magnify particles found at a crime scene by as much as 200,000 times. Sophisticated machines and new procedures help scientists identify chemicals found in complex mixtures.

To begin, fibers are first determined to be natural, manufactured, or a mix of both. Then analysts compare shape, dye content, size chemical composition and microscopic appearances. A phase-contrast microscope reveals some of the structure of a fiber, while various electron microscopes either pass beams through samples to provide a highly magnified image, or reflect electrons off the sample’s surface.

Color

As any fiber analyst knows, color in a product is produced by mixing dyes. There are few "pure" colors. In a chemical laboratory, the color blue is never purely blue. The different ways in which manufacturers create their colors can aid in fiber identification and comparison. An instrument called a microspectrophotometer is used to create a "spectral fingerprint" of the color. When different dye analysis shows two color fingerprints as being identical, it is very strong evidence for proving that two fibers found in different places are from the same source.

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Painting the Scene of the Crime

by Andrea Campbell

The FBI has a library of paint samples and the National Automotive Paint File contains more than 40,000 original paint finish samples. This tremendous stock of material enables examiners to identify the year, make and model of any car by comparing the physical characteristics and chemical composition of paint found at a crime scene with that of known specimens. The chemical constituents of paint can be analyzed via releasing gases and using gas chromatography. This technique creates characteristics for each layer and establishes points of comparison. Also the shape of a chip can be matched to an area where the chip is missing.

With x-ray fluorometry, by bombarding the metal elements in the paint with high-energy electrons, an inner orbital electron of the atom hit by the beam is displaced or knocked out. In order to stabilize, an outer orbital electron falls to fill the void. The atom emits an x-ray and the x-ray emitted is specific to the atom (and therefore the element) that it came from. This technique permits examination of the composition of the paint on an atomic level. The elemental composition of the fragment should match that of its place of origin—allowing the fragment to be linked back to the crime scene.

Although a few flakes of paint may not seem like much, in cases with hit-and-run injuries they can make all the difference.

A ten-year-old Los Angeles boy was killed by a hit-and-run driver. Examiners took the boy’s clothes into an airtight scraping room and carefully rubbed paint off with a metal spatula. Tiny paint chips fell off the boy’s pants, which had probably been pressed into the clothes by his blood and fluids. The gold metallic paint identified was used on three model cars by the same manufacturer. The lab quickly notified the Los Angeles police department that the killer would be driving one of these models.

Soon after, police discovered one of the boy’s neighbors drove a gold sports car with a recently replaced hood. The suspect claimed the body work was the result of a different traffic accident. To his dismay, the hood was recovered, and the examiners were not only able to match the paint chips but they also found fibers caught in the metal that matched the boy’s jacket. Faced with this evidence, the owner of the car confessed to the crime.

Basically, paint can provide key information in any crime whenever a car is a component. A bank robber team in San Diego made the mistake of bumping into a parked car in their attempt for a quick getaway. After the smudge was identified, the motor vehicle bureau helped by providing a list of everyone in that area who owned that particular model. The foreign paint found on the parked car led directly to the apprehension of the harried bank robbers.

In addition to the collections of paint samples, the FBI has standards against which to test typewriting samples, watermarks, plastics and polymers, duct tape, gemstones, cosmetics, and even lubricants like eighty-five types of petroleum jellies. Anything that can be used to build a bomb or aid in a crime is compared microscopically, microchemically, and instrumentally. All specimens have to be identified using two different scientific methods and following established protocols, before it can be used in court.

As forensic science advances with computers and increasingly more accurate means of detecting the component parts of small samples, trace evidence may soon play even more significant roles. As it is, the more trace evidence an investigator can collect at a crime scene, the better the chances of making a case.

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Bad Hair Day?

by Andrea Campbell

I often get forensic science questions from readers. This one is about hair analysis.

Q.: What problems are there in comparing hair samples with hair from suspects nearly 40 years later? Color, texture, resilience and size of shaft are going to be different. My assumption is that the basic DNA will not change. Will microscopic examination of such widespread samples show anything?

A.: A true forensic approach to hair examination will reveal that it is not yet possible to individualize a human hair to any single head or body. Over decades, scientists have tried to find a way to pinpoint the physical and chemical properties of hair, so that it could be used as an individual characteristic of identity. These efforts fail because there is no one property that remains consistent with time or is uniform throughout the head or body. It is said that the color and structure of hair are its most characteristic features, because its chemical properties are not relevant for forensic distinction.

Saying that does not mean that hair has no value as physical evidence; it does. When hair is properly collected at a crime scene, and the laboratory tests are accompanied by an adequate number of controls, hair provides strong corroborative evidence for placing an individual within the vicinity of a crime. It is usually placed in the category called “trace evidence,” along with fibers and other minutiae.

In the question as posed above, hair is a smashing good witness over time because its best two features are: its capacity to hold up against chemical decomposition, and its ability to retain structural features over a long duration.

Animal or Human?

The forensic goal for hair evidence in a criminal case usually involves two questions. Is it human or animal hair? And, secondly, how does the hair found at a crime scene compare with hair from a particular individual?

The first question—animal or human—is answered with the help of the medulla. The medulla is a collection of cells resembling a canal running through a hair. In most animals, this canal is a predominant feature, occupying more than half of the hair’s diameter. The medullary index measures the diameter of the medulla relative to the diameter of the hair shaft and is normally expressed as a fraction. For humans, the index generally has a value less than 1/3. For animals, the value is 1/2 or greater.

Not all hairs have medullae—head hairs generally exhibit none, or have fragmented ones with one exception, the Mongoloid race (this is to say, Asians, American Indians, Eskimos, etc). Their head hairs usually have continuous medullae. The shape and form of medullae, referred to as medullation, is different for different species as well. Under a microscope, they look like distinct patterns: a cat’s, for example, resemble a string of pearls. There are reference standards that scientists use to differentiate, and, of course, experience helps in their evaluations.

A more common request in a forensic investigation is whether or not scalp or pubic hair from the crime scene compares to a suspect’s hair. The evidentiary value boils down to the degree of probability with which the examiner can associate the questioned hair with the known sample.

Hair's Characteristics

A comparison microscope is an invaluable tool, in that it allows the technician to view the questioned hair alongside the known sample. Because hair from any part of the body exhibits a range of characteristics, it is necessary to have an adequate number of known hairs that are representative of all its features when making a comparison.

The criminalist is particularly interested in matching the color, length and diameter. Other important features are the presence or absence of a medulla and the distribution, shape, and color intensity of the pigment granules present in the cortex. Under a microscope you will also be able to distinguish dyed or bleached hair, and detect the presence of fungal or nit infections.

It is pretty easy to figure out the body area of a hair because scalp hairs show little diameter variation and have a more uniform distribution of pigment color. Pubic hairs (yes!) are short and curly; with wide variations in shaft diameter and mostly have a continuous medullae. Beard hairs are coarse and customarily triangle in cross section, with blunt tips from all the cutting and shaving.

The age of a person cannot be determined from hair other than with babies who have fine hair and fine pigment, whereas, a gray hair is fairly characteristic on its own.

But it is possible to determine if hair was forcibly removed. If a hair root is found to have follicular tissue (root sheath cells), that hair may have been pulled or brushed out. Naturally falling hair will show a bulbous-shaped root but will be free of any adhering tissue.

The current examination techniques of hair specimens still rely on mostly morphological characteristics, although the feasibility of recovering DNA from hair and typing a segment is now possible. This method utilizes a technique called polymerase chain reaction (PCR). It amplifies the small amount of DNA found in the human hair root (follicle tissue). The actual success rate for DNA typing is in the area of 34% for case samples.

In 1996, the FBI initiated a program to compare human head hair and pubic hairs through DNA analysis. This type of DNA analysis is called mitochondrial DNA and is located within the nuclei of body cells. The DNA is transmitted only from mother to child. It can be used when the amount of DNA present is small or degraded.

Hair is class evidence and it is not possible except in rare cases to determine that a questioned hair sample came from a particular individual to the exclusion of all others. The examiner to a large extent must rely on his experience and a statistical probability. They may say something like, “In my opinion, the representative hairs revealed that the odds of two similar pubic hairs originating from two different individuals are about 800 to 1."

Collecting Hair

To collect hair evidence, one usually collects about 50 full-length hairs from all areas of the scalp for a representative sampling. A minimum collection of two dozen full-length pubic hairs should cover the range of characteristics present in that portion of the body. In rape cases, a clean comb is used to capture all loose foreign hair present in the pubic area before the victim is sampled for control hair. The comb is then packaged in a separate envelope. And, a criminalist would not collect, nor compare, head hair with pubic hair—separate is the watchword here.

As a routine procedure, hair samples are collected from a victim of suspicious death during an autopsy. Failure to make this simple collection at an opportune time may result in complicated legal problems at a later date.

Test your knowledge with a mini-quiz at this interesting Web site.

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