Most of us won�t be on the jury of a forensics-based trial or be accused of a
crime, but for those that are, and for those who regularly watch true crime
documentaries, it should be known that many of the forensic techniques we
grew up hearing about are not actually accurate.

Earlier this year, ProPublica published an article that included a list of
things to look out for when determining whether forensic analysis is sound
science or junk science. The list includes:

� It has limited or no scientific evidence or research supporting it.

� It is presented as absolutely certain or conclusive, with no mention of
error rates.

� It relies on subjective criteria or interpretation.

� It oversimplifies a complex science.

� It takes just a few days to become an �expert.�

With this information in mind, let�s take a look at some forensic techniques
that have been featured in movies, television shows, and true crime
documentaries but that are actually not sound science at all.

Bite Mark Analysis
Serial killer Ted Bundy was convicted in part on bite mark analysis, and the
technique was used in the following decades. In recent years, however, the
technique has been widely criticized as unreliable, though it is still used
in courtrooms.

Bite mark analysis falls under the broad terms of forensics known as pattern
matching, where an �expert� looks at evidence collected at a crime scene and
evidence taken from a suspect, compares the two, and makes a subjective
determination as to whether there�s a match.

At least 35 people have been wrongfully convicted based on bite mark
analysis, The Intercept reported last year, including Steven Mark Chaney, who
was convicted in 1987 for a murder he didn�t commit. Chaney had nine alibi
witnesses and there was no actual evidence linking him to the murders of John
and Sally Sweek, but two forensic dentists testified that an alleged bite
mark found on John�s arm matched Chaney�s teeth.

Journalist Radley Balko has extensively documented the problems with bite
mark analysis, questioning how accurate it could possibly be.

�For example, we don�t know what percentage of the human population�s teeth
are capable of leaving a certain pattern of marks on human skin,� Balko wrote
last month. �We don�t even know if such a calculation is even possible. And
if it were possible, we don�t know that human skin is capable of recording
and preserving bite marks in a way that�s useful (the studies that have
examined this suggest it isn�t).�

�The characteristics of a bite mark could be affected by the angle of the
biter�s teeth, whether the victim was pulling away at the time of the bite,
the elasticity of the victim�s skin, the rate at which the victim�s body
heals, and countless other factors,� he continued.

Cadaver Dogs
Many cases use dogs who are trained to detect the scent of dead bodies to
determine whether a crime has occurred and to connect suspects to that crime.
But their accuracy has been called into question in recent years. In some
cases, dogs have found scents that couldn�t possibly have existed.

Take the missing girl Madeleine McCann. Her parents were labeled suspects in
her disappearance four months after their daughter vanished, based largely on
a cadaver dog indicating the scent of death on one of McCann�s baby toys and
on her mother�s clothes.

The problem, however, is that it is unclear whether McCann was even killed,
but speculating that she was killed the night she died, the cadaver dogs
would have had to pick up minute traces of a scent four months after the
murder. As Slate reported in 2007, it is unclear how long that scent could
linger, with a former Scotland Yard dog handler suggesting the scent wouldn�t
last longer than a month.

And to be clear, the dogs didn�t actually find any human remains.

Some attorneys have convinced a Wisconsin judge that some of these death-
sniffing dogs were accurate just 22-38% of the time. Even prosecutors who
denied those attorneys� claims said the dogs had a success rate of just 60-
69%, which is hardly accurate enough to convict someone.

A cadaver dog was also used as evidence against Scott Peterson, who was
convicted in 2004 of killing his wife, though many question whether he could
have actually been the murderer.

In the Peterson case, a trailing dog (similar to a cadaver dog but trained to
follow scents in the air) allegedly followed his wife�s scent from a parking
lot at the Berkeley Marina, where Peterson kept a small fishing boat, to a
nearby pier. The dog allegedly followed this scent four days after Peterson�s
wife, Laci, was reported missing. The dog was given Laci�s sunglasses and
hairbrush, both of which could have had cross-contamination from Scott
Peterson, who had maintained his innocence and told police he went fishing on
the day Laci went missing.

Contact or Trace DNA
When we hear the letters DNA, we immediately think science and indisputable
fact, but there is a type of DNA evidence that is not reliable and has been
used to wrongly imprison many � contact, or trace DNA.

We leave behind trace amounts of DNA on everything we touch. This is called
contact DNA. It may only be a few skin cells, but it is there. That contact
DNA can then be transferred to another surface without us touching it. For
example, if you shake someone�s hand, they�ll have traces of your DNA left
behind, and then if they touch something else, they could leave those traces
of your DNA as well as their own DNA on that object.

There isn�t as much DNA left behind as there would be in blood, saliva, or
semen, yet �experts� have used contact DNA to put people in prison. One
example is the case of Mayer Herskovic, who was convicted in 2017 for
allegedly taking part in a multi-person attack against a young, gay black man
in Brooklyn in 2013. Experts testified that trace amounts of Herskovic�s DNA
was found on one of the victim�s shoes. To come to this conclusion, the crime
lab had to take a tiny sample of the DNA and replicate it to get a useable
sample. This involved copying the DNA and then copying the copies thousands
of times, and then running that data through the computer to get statistics
claiming it was highly likely that the tiny amount of DNA on the shoe
belonged to Herskovic.

The problem is that the technique, which is no longer used by the crime lab,
didn�t find the victim�s DNA on his own shoe, but also found the DNA of
someone else. And because the community where the crime occurred was largely
homogenous, the DNA results could have matched someone other than Herskovic.
Herskovic�s conviction was overturned in 2018.

911 Call Analysis
Police and prosecutors sometimes train in 911 call analysis, which claims to
detect a murderer in a phone call by listening to their speech patterns,
tone, word choice, and other factors when calling authorities, ProPublica
reported.

The technique was designed by Tracy Harpster, a retired deputy police chief
with limited homicide investigation experience and little scientific
background. He used a small study to create the technique for his master�s
thesis, and it was soon accepted by law enforcement nationwide. The technique
includes a checklist of how many �errors� a person commits during a 911 call,
which Harpster said gives away their true involvement. Asking �huh?� in
response to a question from a dispatcher is one indication of guilt, as is
saying �please� by itself. If a person doesn�t seem urgent enough, that is
also an indication of guilt, Harpster concluded.

Studies from the FBI in 2020 and 2022, however, warned against the technique,
saying its findings could not be corroborated and that it may simply create
bias against the accused.

The technique was used to convict Jessica Logan of killing her baby in 2019.
Logan�s baby had died during the night and she called 911 frantic. She was
crying and screaming and could barely speak to the 911 operator. Detective
Eric Matthews determined her agony was fake and that she had actually killed
her own baby.

Matthews had taken a two-day course on 911 call analysis, and used what he
learned to get Logan convicted. Many are questioning her conviction.

Firearm Analysis
We�ve all seen images of experts comparing the lines of one bullet, referred
to as rifling marks, to the lines on another bullet. This is firearm
analysis, the belief that every gun in the world contains minute
imperfections that distinguish it from every other gun on the planet, just
like DNA.

But there�s no evidence this is true. It is unknown whether marks in the
gun�s barrel leave unique marks on bullets that no other gun can recreate,
Radly Balko wrote last month. He also raised other questions regarding
firearm analysis.

�We don�t know if a gun�s firing pin and ejection mechanism leave unique
marks on a casing,� he wrote. �We don�t know the frequency with which
specific marks may appear among the entire population of fired bullets. We
also don�t know how to account for the likelihood that a gun will leave
different sorts of marks on bullets over the course of its life as a
functioning gun as the ridges and grooves inside the barrel wear down � an
issue that would presumably affect older cold cases.�