In the profession's early years, forensic anthropologists
worked mostly in labs, and detectives delivered suspicious material
-- remains, usually -- by hand. But poking around in the soil where
a body is found can tell you a lot about when, and how, a person
Crucially, experts can get a first guess at
time since death. "Back in the 80s, forensic entomology was the only
way to determine time since death after a few days," says Arpad
Vass. "Since then, we've developed models that refine what we know
about the postmortem interval."
As bodies decompose, they leak five fatty
acids -- the breakdown products of muscle and fat -- into the ground.
Since the profiles of these acids vary as time passes, analyzing
them can reveal how long a body has been dead and pinpoint how long
a body has been lying in a particular place. Vass has developed
two methods for dating remains by looking at these compounds.
The first traces the ratio of the five fatty
acids -- a method that works as long as there is soft tissue (skin
and organs) on the body. If not, another technique tracks the ratios
of seven inorganic compounds, such as sodium and calcium, which
leach into the soil from the bones. If a body is too badly decomposed
for those techniques, scientists rely mostly on bones.
We'll get back to bones later, because there's
still a lot to do at the crime scene. If the surrounding soil does
not contain the telltale chemicals released as a body decays, the
body was probably placed there recently. Soil samples containing
those chemicals and the bugs that help experts guess how long it
has been since the person died. This number can be the key to whether
an alibi flies or flops in a murder trial.
Sounds easy enough. But temperature, humidity
levels, and grave depth can all change how fast a body decomposes.
The fastest transformation from corpse to skeleton at the Body Farm
happened in just 12 days. But if a person is buried two feet underground,
total skeletonization can take six months, Jantz says. A body six
feet under takes more than two years.
A body will also skeletonize faster if it
is buried in acidic ground. (Soil in pine forests tend to be far
more acidic than soil in deciduous forests.) And "perps," says Vass,
are getting better at warping bodies and burial sites to confuse
investigators. Vass suspects they learn tricks -- like spraying insecticide
on a body to ward off insects -- from TV shows like CSI.
It creates a big scientific headache when that
happens, Jantz says, because bugs make great witnesses. We know
we promised to stick to anthropology, but forgive us for a little
digression. The American Board of Forensic Entomology lists only eight members,
but their work is key in crime-solving.
Only two dozen types of insects eat rotting human flesh. The two
stars are the carrion feeders (Calliphoridae)
and the flesh flies (
Sarcophagidae). Distinguishing the three larval stages
is often the first step in determining how long a body has been
By comparing species found on a body with those in the area, forensic
entomologists can also figure out whether a body was moved.
DNA fingerprinting can be used to identify insect species or,
sometimes, human content found in their guts. (See "A DNA-based
approach..." in the bibliography).
a decomposing body, and the bugs that inhabit it, reveal plenty,
secrets remain in the bones.
"Bones are the last chance that individuals
have to say what their lives were like," says Galloway. "Written
into your bones are the things you do repeatedly, the injuries you
suffered, how you died, how old you were."
Sometimes a corpse is too long dead to give
more information than can be gleaned from the bones alone. Sometimes,
only bones remain. And DNA profiling can identify bodies and place suspects at a crime
scene. But to identify a body, detectives also need a DNA sample
to compare to the remains. Often, too little is known about the
body to gauge who it might have been.
Mass graves like this are often found years
after burial. Investigators rely on forensic anthropologists to
glean information from the bones left behind. Courtesy
Arpad Vass, Oak Ridge National Laboratory
Enter the bone laboratory. Inside, there are
some impressive new tools. But some things -- like cleaning the bones
-- will always be macabre, says Galloway.
"We put bones in a box of dernestid beetles
-- carrion beetles that will only eat dry, leathery, soft tissue
but don't damage the bones at all," she explains.
When there is special urgency or the bugs
are busy, Galloway or her graduate students simply boil the bones
clean with water and a detergent. "You cook it until you can pull
off the soft tissue," she says, recalling an occasion when she accidentally
poured a bit of the "soup" in her lap.
Once the bones are clean and dry, the first
step is to determine whether they are human. To the untrained eye, bones from deer or
goats can be hard to tell from human bones, and
it can be almost impossible for anyone but a seasoned osteologist
to identify the fragile fragments of a human hand or wrist.
The next question is whether the bones are
connected to a crime. The site might be of use to historians or
archaeologists but not forensically significant. If so, and the
body cannot be identified by DNA analysis, the next step is to create
a biological profile.
Looking at the teeth can reveal the age if the remains belong
to a child or adolescent. Human teeth break through in a predictable
pattern and offer a fairly reliable estimate between five months
and 21 years.
The epiphyseal union -- areas of the femur that gradually fuse
as a person ages -- can help estimate young ages if the teeth are
The skull and pelvic girdle are two giveaways in determining sex.
Male and female skulls show some differences, but the pelvic girdles -- a woman's is wider than a man's -- are the dramatic identifiers of sex.
Scientists guess at stature based on the long bones of the legs,
when they are available. If not, a range of height can be established
from nothing more than a single finger or foot bone.
Judging ancestry is difficult and controversial.
Nevertheless, skeletal attributes, such as the ratios of certain
skull bones to one another, can hint at a particular background.
These estimates are far more accurate now
than twenty years ago, Jantz says. Part of the Body Farm's mission
is to save the skeletons left behind after bodies decompose.
Researchers use the archives (a similar facility
exists at the University of New Mexico) to ask questions about how
the human skeleton is changing over time.
"The collection now has 500 in it, and it's
growing at rate of 50 a year. Ten years will be 1000, if current
trends continue," explains Jantz. "There are lots of skeletons of
19th Century Americans, but these are the only modern collections."
The skeletal archives also help researchers
devise new methods for creating biological profiles based on bones.
"You might have an idea that you think this particular feature would
work well as a sexing device or to estimate age or whatever," notes
"For our skeletons, we know age, sex, race,
height, and weight...so you can test your hypothesis about estimating
some component of what a person was like in life -- which is the
basic activity of forensic anthropology."
are more than 200 bones in the human body. To the trained eye, even
the smallest of them can reveal telling details about the person
who left them behind. Image: NIH.
Another archive consists of data but no actual
bones. In the early 1980s, Jantz and his colleagues initiated a nationwide
program that allows anthropologists to record information about
their cases -- skeletal measurements, for example -- in a computer
database. The database now has information from more than 2,000
"It has the advantage of having considerably
more skeletons, but the disadvantage that you can only examine things
for which we have data. You can't go back to the skeletons," Jantz
You may know about sketch artists who draw pictures
of criminals based on witness descriptions. Anthropologists do the same
thing using skeletal remains. Forensic artists build models of what
a dead person might have looked like by making a plaster cast of
the skull and covering it with clay to imitate flesh.
In recent years, computer scientists have
been lending a hand. Researchers at the Max Planck Institute for
Computer Science in Germany, for instance, have been working on
a three dimensional graphics
program to produce better likenesses.
Researchers scan a skull to create a 3D computer
model. Certain sites on the skull reveal qualities of the flesh
that would have covered it. The software automatically adds flesh
of appropriate thickness, adjusting for whatever variables -- such
background -- are already known. The software, which is still
in development, uses a template that includes the 24 facial muscles
responsible for our expressions, producing an animated head with
an almost-lifelike level of detail.
How to do death for