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impressions and footprint casts taken from a suspect.

Similarly, a link to footwear matched to a crime scene

can be determined by comparing the insoles of the

crime scene footwear to footwear seized from a sus-

pect, or to inked impressions and casts taken from

a suspect.

Introduction

Barefoot morphology comparison refers to the exami-

nation of the weight-bearing areas on the bottom of a

human foot, when ridge detail is not present, to estab-

lish a link between the bare foot of an individual and

a footprint impression found at a crime scene [1–3].

In the case of footwear linked to a crime scene, com-

parison can be made to shoes seized from a suspect, or

to inked impressions or casts taken from a suspect.

Research has indicated that the shapes of footprints

are sufﬁciently variable to make it possible to include

(as having possibly made the impression) or exclude

(as deﬁnitely not having made the impression) a sus-

pect as being the person who created a particular

footprint at a crime scene [3]. As an example, Fig. 1

show barefoot impressions taken from identical twins,

illustrating that even twins can be differentiated based

on their footprints.

When a crime scene is being examined, it is com-

mon to ﬁnd footprints that might be those of the

perpetrator of the crime. If ridge detail is developed

in a barefoot impression, the comparison to a suspect’s

foot can be carried out in exactly the same fashion as a

ﬁngerprint comparison [4, 5]. If enough ridge detail,

with sufﬁcient clarity, is available for comparison, a

positive identiﬁcation may be forthcoming. However,

if the barefoot impression is smudged or unclear for

any other reason, or if it is a socked impression,

then recourse can be made to barefoot morphology

comparison.

Similarly, when a shoe has been positively identi-

ﬁed back to a crime scene, and no suspect has been

found in possession of the footwear in question, re-

course can again be made to barefoot morphology

comparison. This can be accomplished by comparing

the impressions on the insole inside the crime scene

shoe to the impressions inside a similar shoe worn by

the suspect, or to inked impressions and casts seized

from the suspect.

The comparison itself is similar to a toolmark or

tire track comparison, where the foot has acted like a

tool or a tire in creating an imp ression at the

crime scene. The shapes of various parts of the foot

are com pared to se e if there is correspondence

between the crime scene impression and the suspect

exemplars. In a footwe ar examp le, the imp ression to

be compared has been made on the insole of the

identiﬁed footwear.

Background

Although footprints in gen eral look quite similar,

it has long been assumed that careful examination of

barefoot impressions could be used to differentiate

between people. Historically, in various societies,

trackers have been trained to be able to pick up some-

one’s trail and to follow the person based on their

footprints [3].

Footprint evidence was presented in court as early

as the late nineteenth century, when a criminal w as

convicted in 1888 based on his footprint. Other cases

have since been documented in the forensic literature,

mainly from Europe and North America [6]. Much of

this early casework was based on the assumption that

Forensic Barefoot Comparisons. Figure 1 Barefoot

impressions taken from identical twins, illustrating the

variability of footprints, even for twins.

570

Forensic Barefoot Comparisons

footprints were unique to the individual, without

many studies to support this hypothesis.

Whenever a new means of including or excluding

suspects is being introduced in court, the basis for the

comparison must be justiﬁed. Some early work on foot-

print variability was carried out in India [7], while in

North America, Dr. Louise Robbins, an anthropologist,

carried out studies on the individuality of footprints in

the 1970s [8 ]. In the 1980s, the Federal Bureau of

Investigation (FBI) collected and compared footp rint

impressions from hundreds of volunteers to show how

variable barefoot impressions might be [9, 10].

The Royal Canadian Mounted Police (RCMP)

began research in this area in the 1990s [11]. Inked

barefoot impressions were collected from thousands of

volunteers for entry into a computerized database. As

each footprint was measured and entered, it was com-

pared with previous impressions in the database to

ensure that another foot did not share the same mea-

surements. A statistical analysis of the impressions was

carried out to illustrate how variable barefoot impres-

sions are [12]. Even with a limited number of samples

and measurements, probabilities on the order of 1 in

a billion were achieved.

Collecting Evidence [3]

When a bare or socked foot impression is found at a

crime scene, the investigator must document the evi-

dence correctly. Photographs, with a scale included,

should be taken. If required, barefoot impressions can

sometimes be enhanced in situ using ﬁngerprint pow-

der or chemical techniques, especially for impressions

in blood. Impressions can then be lifted, or, depending

on the surface, the entire impression can be removed

from the scene. All of this evidence will have to be sent

to the expert who is doing the ﬁnal barefoot morphol-

ogy comparison.

Similarly, when footwear impressions are found,

they should be thoroughly documented. Again, en-

hancement techniques can be used to make the

impressions more visible. If accidental characteristics

are noted, there is the possibility of positively linking a

shoe to the impression found at the crime scene.

If a suspect is arrested, his feet and his foot impres-

sions must be well-documented. Several photographs,

including a scale, should be taken of the feet to ensure

that the tops, sides, and bottoms are all recorded. Foam

impressions should be taken for la ter casting. Inked

standing and walking impressions should also be

obtained. Standing and walking impressions should

also be obtained with the suspect wearing a pair of

socks.

If the case involves footwear impressions, attempts

should be made to seize similar footwear from the

suspect. The best comparison would be of a shoe

insole with another shoe insole. However, the feet of

the suspect should also always be recorded in the

same manner as described above.

The Comparison Process [3]

Barefoot morphology comparison should only be

undertaken by an adequately-trained specialist. The

RCMP has conducted barefoot comparison courses in

North America and Europe, training forensic specia-

lists from several countries. A group of doctors has

recently formed a forensic podiatry sub-committee

within the Internat ional Association for Identiﬁcation

(IAI), currently establishing its own criteria for train-

ing and standards.

As in any other physical comparison, class charac-

teristics are compared ﬁrst. The overall size of the foot

and the number of toes making contact with the

ground would be considered class characteristics, and

can be used to quickly eliminate a suspect foot.

The shape and placement of the toes, the shape

of the

▶ metatarsal ridge, the length and width of the

arch, and the contour of the heel can be examined and

compared (see Fig. 2). Any unexplained feature can

be used to eliminate a suspect, while correspondence

of features means that the suspect foot remains

included as a possible source of the crime scene im-

pression. Some examiners will make positive iden-

tiﬁcations based on foot morphology [13 ], while

others will only go as far as a strong likelihood that

the same foot made both the crime scene print and the

exemplar [3]. Because the uniqueness of barefoot

impressions has not been proven, and crime scene

and inked impressions are not exactly reproducible,

current RCMP policy advises examiners against

making positive identiﬁcations. Positive identiﬁcations

may be possible when ﬂexion creases, marks, and scars

are visible [14].

When the impression is three-dimens ional, like

a footprint in mud, it is important to try to obtain a

Forensic Barefoot Comparisons

571

three-dimensional replica of the suspect’s foot for

comparison. The use of foam impression material

and dental casting material should be considered.

In the case of footwear that has been positively

identiﬁed back to the crime scene, and where footwear

has be en seized from the suspect, the outer areas of the

shoe can be examined to conﬁrm that wear on the

shoes is similar. The barefoot impressions made on

the insoles can then be compared in much the same

fashion as the barefoot comparisons described above.

The inside uppers of the footwear can also be exam-

ined to look for agreement or disagreement of wear

and damage. If footwear cannot be seized from the

suspect, then the examiner must make-do with inked

impressions and casts of the suspect’s bare feet, bearing

in mind the changes in morphology caused by the foot

being constricted in the shoe.

In Court

Barefoot morphology comparison is not yet a rou-

tinely-accepted forensic technique. As such, it is still

vigorously challenged when it is presented in court.

In Canada, the testimony has been successfully

defended in Mohan and Voir Dire hearings [15],

(R v Dimitrov was overturned because the jury

put too much emphasis on ‘‘could have been’’ testimo-

ny, and not because of the technique itself) while in

the US it has withstood the scrutiny of ‘‘Rule 702,’’

Frye, and Daubert challenges. An early case that was

sent back on appeal when the judge felt that not

enough background research had been done has been

successfully re-tried in light of more recent published

research. In essence, the courts have started to

recognize the scientiﬁc foundation upon which the

evidence is based.

Besides Canada and the United States, barefoot

comparison testimony has been tendered in several

countries around the world. In Israel, barefoot

morpholog y comparison testimony was appealed

all the way up to the highest court, and upheld.

As the technique becomes more accepted, prosecu-

tors and defense lawyers w ill soon start to look for

opportunities where this type of evidence might be

useful.

Conclusion

Barefoot morphology comparison refers to the com-

parison of the weight-bearing areas of feet in an effort

to include or exclude a suspect as being linked to a

crime scene. Background research has established the

variability of barefoot impressions, justifying their use

in a forensic context. Crime scene investigators should

be aware of this technique and should always be look-

ing for suitable evidence of this kind.

Related Entries

▶ Earprints

▶ Fingerprints

References

1. Bodziak, W.J.: Footwear Impression Evidence, pp. 381–411. CRC

Press, Boca Raton, FL (2000)

Forensic Barefoot Comparisons. Figure 2 Comparing the toes and the contour of the metatarsal ridge.

572

Forensic Barefoot Comparisons

2. Kennedy, R.B.: Bare footprint marks. In: Siegel, J.A., Saukko, P.J.,

Knupfer, G.C. (eds.) Encyclopedia of Forensic Sciences,

pp. 1189–1195. Academic Press, London (2000)

3. Kennedy, R.B., Yamashita, A.B.: Barefoot morphology compar-

isons: a summary. J. Forensic Ident. 57(3), 383–413 (2007)

4. Lemieux, M.: Histoire de Pied/a foot story. Identif. Can. 25(4),

16–17 (2002)

5. Watkins, D., Brown, K.C.: The case of the toe print. J. Forensic

Ident. 57(6), 870–873 (2007)

6. McCafferty, J.D.: The shoe ﬁts. The Police J. 28(2), 135–139

(1955)

7. Puri, D.K.S.: Footprints. Int. Police Rev. 187, 106–111 (1965)

8. Robbins, L.M.: The individuality of human footprints. J. Forensic

Sci. 23(4), 778–785 (1978)

9. Lovejoy, O.C.: Methods of Footprint Analysis. Seminar in Foot-

print and Shoeprint Identiﬁcation. Federal Bureau of Investiga-

tion, 29 April 1984

10. Bodziak, W.J., Monson, K.L.: Discrimination of individuals by

their footprints. Paper presented at 11th meeting of Internation-

al Association of Forensic Sciences, Vancouver, BC (1987)

11. Kennedy, R.B.: Uniqueness of bare feet and its use as a possible

means of identiﬁcation. Forensic Sci. Int. 82(1), 81–87 (1996)

12. Kennedy, R.B., Chen, S., Pressman, I.S., Yamashita, A.B.,

Pressman, A.E.: A large-scale statistical analysis of barefoot

impressions. J. Forensic Sci. 50(5), 1071–1080 (2005)

13. DiMaggio, J.A.: The Foot as a Forensic Tool. Paper presented at

the 55th annual meeting of the American Academy of Forensic

Sciences, Chicago, IL (2003)

14. Massey, S.L.: Persistence of creases of the foot and their value for

forensic identiﬁcation purposes. J. Forensic Ident. 54(3),

296–315 (2004)

15. Richard, C.: Case law: [2002] Ontario superior court R. V.

Arcuri. Identif. Can. 25(4), 18–20 (2002)

Forensic DNA Evidence

T. HICKS,R.COQUOZ

Institut de police scientiﬁque, Ecole des sciences

criminelles, Lausanne, Switzerland

Synonyms

DNA analysis; DNA proﬁling; DNA typing

Definition

Deoxyribonucleic acid (DNA) is a large molecule present

in all living cells (e.g., animals, plants, viruses). As a tape

allows the storage of a recording, DNA allows the storage

of genetic information. It consists of two long chains of

nucleotides twisted in a double helix. There are four types

of nucleotides designed by the name of their bases:

Adenine (A), Guanine (G), Cytosine (C) and Thymine

(T). The genetic information is encoded in the sequence

of nucleotides of the DNA molecule. Part of its name

originates from its localization in the nuclei of the cell.

However, the acronym is also used for

▶ mitochondrial

DNA (mtDNA), which is the DNA present in the

mitochondria of the cells. It is transmitted only by

the mother.

Introduction

Although DNA proﬁling has high discriminating

power and can help establishing the biological identity

of a person, it is not used as a biometric yet. Indeed, the

results of the analysis are not immediate (nor yet

amenable to full automation), the cost of analysis is

high, and there are contamination and transfer issues.

Moreover, as parents transmit biological material

to their children, DNA can be intrusive and reveal

unknown family relationships.

Most of the text that follows is based on [1].

Another standard text in English is [2].

DNA: Basic Concepts

Each human cell contains biological information; each

of the cells thus contains the same DNA. As DNA is

a very long molecule (three billion base pairs), it is

organised into 23 small bundles: the chromosomes.

Each child receives two DNA: one from the mother

and one from the father. Each person (and each cell

from this person) has thus two copies of each chromo-

some, one from the mother and one from the father,

giving a total of 46 chromosomes. They are numbered

in pairs from 1 to 22, the 23rd pair being the sex

chromosomes X and Y. On each of the chromosomes,

there are genes (i.e., a zone where the DNA codes how

to make a protein). The number of genes is estimated

to be around 20,000–25,000. When reading DNA from

one extreme to the other, one will encounter a code

‘‘START’’ to indicate that one can read from here how

to make a given protein, and a code ‘‘STOP’’ to indi-

cate that this is the end of the genetic information

necessary for that protein. The code for the following

protein does not begin immediately after the ‘‘STOP’’

Forensic DNA Evidence

573

message and there are usually several thousands

nucleotides in between that do not code genetic infor-

mation. These are called noncoding DNA or junk DNA

and represent 98% of the genetic material. The geo-

graphical distribution of the genes and the noncoding

DNA is in principle identical across all individuals in a

given species.

A geographical nomenclature has been derived to

designate a given localization on the DNA strand of

human chromosomes: the locus (pl. loci). For each

locus, one copy is received from the father and one

copy from the mother. These two copies are called

alleles: therefore for each locus, a person will have

two alleles. The set of alleles owned by a person for a

locus is called his/her genotype. If the alleles transmit-

ted by the father and the mother are the same, the

individual is homozygote for this locus. If the two

alleles transmitted are different, then the individual

will be heterozygote at this locus. The loci are symbo-

lized by a four-digit code, that is particularly useful for

noncoding DNA. The ﬁrst letter of the code is D (for

DNA), the second is the chromosome number (1, ...,

22, X, Y), the third element indicates the sequence type

(S: a unique sequence; Z a sequence that has several

copies, at different localizations, on the same chromo-

some; F a sequence that is part of a family with similar

sequences that are encountered on several chromo-

somes); the last digits are a unique number that gener-

ally correspond to the order in which the sequences

were discovered. As an example, the locus D18S51 is a

DNA region on chromosome 18, with the serial num-

ber 51. This locus is commonly used in forensics be-

cause of its polymorphism and is present in different

commercial kits (e.g., SGMplus ABI; Powerplex 16

Promega).

Since DNA is stable over the lifetime of an individ-

ual, and is reasonably resistant to chemical degra-

dation, it is a good candidate for use in forensic

science. One must further ﬁnd a sensitive and not

too expensive technique that enables the analysis of

parts of the DNA that vary between individuals: the

genetic markers. These markers should show as much

as polymorphism as possible. There are two types of

polymorphisms: sequence polymorphism (the nature

of the nucleotides themselves differ from individual

to individual, e.g., mtDNA, SNPs) and length polymor-

phism (the difference between individuals is based

on the length of a given repetitive sequence of nucleo-

tides, e.g., STR).

In 1985, thanks to the discovery of repetitive

sequences, Sir Alec Jeffreys ﬁrst applied the analysis

of DNA to forensic science. As discussed previously,

there are coding and non coding DNA. The repetitive

sequences are zones in the DNA, where noncoding

DNA seems to stutter. The human DNA has a very

large number of different repetitive sequences (30% of

the genome) and the length of the repetitive sequences

varies between individuals. If the length of the repeti-

tive sequence is larger than six nucleotides, one

speaks of VNTR (Variable Number Tandem Repeats,

Nakamura). If it is equal or smaller to six, one will speak

of STR (Short Tandem Repeat). STRs have also

been named microsatellites and VNTRs minisatellites.

Nowadays, STRs are the standard targets of the routine

analysis of forensic samples. Companies offer different

type of kits allowing the analysis of several STRs at

the same time (multiplex STR analysis). An example

of some kits available is given below:

Forensic DNA Analysis

Before analysis, one has to sample the DNA on the

crime scene and to sample the individual. As genetic

information is theoretically the same in every cell,

saliva is generally used for the later. On crime scenes,

chemical tests to detect saliva, sperm, or blood can be

used to help in ﬁnding the invisible stains. If a stain is

detected, the object is either cut, or swabbed. As, it is

possible to detect very low levels of DNA, it is highly

recommended to wear gloves and a face mask when

collecting DNA.

Once DNA has been collected, it will be extracted,

puriﬁed, and quantiﬁed. Because there is often very

little material in forensic samples, the speciﬁc zones

of DNA that are the target of the analyses will be

ﬁrst ampliﬁed using a technique called Polymerase

Chain Reaction (PCR ). PCR is often compared to a

DNA photocopier, where a given DNA segment is

copied a given number of times. First, the zone to

be ampliﬁed is delimited using two primers: one is

placed at the beginning of the sequence and one at

the end. During the copying cycles of the PCR pro-

cess, copies of the original DNA zone will be produced.

After one cycle, there will be the original DNA and

one copy; after two cycles, there will be 2 more copies

and after 30 cycles there will be about a billion

copies (Fig. 1).

574

Forensic DNA Evidence

Multiplex STR Analysis

PCR can be used to copy simultaneously several DNA

fragments: one uses different primers, each corres-

ponding to the DNA zone that has to be copied. This

simultaneous ampliﬁcation of different DNA zones

is called Multiplex PCR. The PCR products are ana-

lyzed using Capillary Electrophoresis. This technique

allows the separation of DNA fragments according to

their sizes while they travel through a thin capillary.

The large fragments move more slowly than small

fragments. A peak is displayed on the results’ graph,

when the detector at the end of the capillary detects

DNA molecules. The detector is able to differentiate

between up to ﬁve different dyes. The detector can

recognize STR alleles that have the same length but

are labeled with different dyes.

Theoretically, one can amplify dozens of different

fragments in one operation, which saves considerable

time. However, the design of multiplex STR analysis

kits is not straightforward: the numerous primers

involved must not interfere with each other; the set

of alleles of one STR must be recognized from the

alleles of the other STRs, either through the use of

different labeling dyes or because they are in different

size ranges. The different STR will be chosen if possible

on different chromosomes, so that the transmission of

the alleles from generation to generation can be con-

sidered independent.

PCR is unable to amplify efﬁciently large frag-

ments. It is thus not possible to increase indeﬁnitely

the number of STR analyzed simultaneously with a

multiplex kit. The practical limit is around 15–20

STRs. An example of a proﬁle obtained with Multiplex

STR analysis is shown below. The vast majority of

forensic DNA analyses done today is multiplex STR

analysis. It is the golden stand ard and fulﬁls most of

the needs of forensic DNA ana lysis.

Figure 2 shows the resu lt of an ana lysis performed

on an individual with the SGMplus kit.

Nonautosomal DNA

An autosome is a nonsex chromosome. Nonautosomal

DNA is a DNA that originates either from a sex chro-

mosome (i.e., X, Y), or from mitochondria (mtDNA).

Sex chromosome DNA is used to study the paternal

heritage: if there is no mutation, a son will have the

same Y chromosome than his brothers, his father, and

his paternal lineage; a daughter will have one of her X

chromosome identical to her father and her paternal

lineage. Mitochondrial DNA is used to study the ma-

ternal heritag e: a mother will transmit her mitochon-

drial DNA to her children, grandchildren, etc. These

markers are useful for parentage testing. Since there are

hundreds of copies of mtDNA per cell, mtDNA can

also be used when the trace is degraded or/and there

is very little nuclear DNA (e.g., hair without roots).

STRY may also be useful in rape cases, when the male

DNA of the agressor is not detected in the DNA proﬁle

because of the presence of vast amounts of female DNA

in the mixture. When speaking of alleles observed for

Y chromosome STR or mtDNA and STRX, one speaks

of haplotype and not genotype, as a person owns

only one single allele.

Forensic DNA Evidence. Figure 1 From [1] representing the PCR Process.

Forensic DNA Evidence

575

Low Template DNA Analysis

In essence, PCR allows a sensitivity at the single molecule

level. However, for the standard DNA proﬁling, the

potential of PCR is curbed to avoid the stochastic effects

and contamination problems associated with an extreme

sensitivity. The sensitivity of standard DNA proﬁling is

thus adjusted to provide a DNA proﬁle only when there

is DNA from at least 50 cells in the evidence material.

The concept of low template level analysis, or as previ-

ously known LCN (Low Copy Number), covers strate-

gies designed to go beyond this limit. The usual strategy

to reach such an extreme sensitivity is to increase the

number of copying cycles of the PCR (e.g., 34 cycles

instead of 28) [3]. Increasing sensitiv ity does not go

without caveats: artefacts arise with alleles dropping in

and dropping out. This added sensitivity also increases

the issue of contamination. The use LCN proﬁles

should induce very strict protocols to avoid contami-

nation on the scene and at the laborator y. It requires

cautious interpretation. In the Omagh Bombing,

the use of low template level proﬁles was challenged,

but was shown to be scientiﬁcally robust in the review

conducted by Professor Caddy, Dr Linacre, and

Dr Taylor [4].

SNPs and DNA Chips

SNPs (Single Nucleotide Polymorphisms) occur on

average every 1,200 nucleotides: that means that

depending on the individual the nucleotide in that

position will differ. In theory there might be four

variants (A, T, G, C) for the nucleotide; however,

because of the reality of the evolution process only

two variants are usually observed. The main caveat

of SNPs is their limited sequence polymorphism.

Multiplex analysis of a large number of SNPs can

however overcome this limitation. SNPs can be ana-

lyzed using miniaturized devices call ed DNA chips.

These are miniaturized systems allowing the analysis

of hundreds of SNPs. The disadvantages of SNPs

are their low polymorphism, and their very limited

capacity to handle DNA mixture cases. SNP analysis

certainly has good prospects for speciﬁc applica-

tions.

▶ Mitochondrial DNA polymorphisms are in

essence SNPs. SNP analysis has better chances of

success for highly degraded samples than STR ana-

lysis. Some speciﬁc SNPs have the capacity to pro-

vide morphological information (hair, eye colour, ...)

and Y chromosome SNPs should be able to pro-

vide useful ethnic information. Some companies

(e.g., 23andme; Decode genetics; ...) have star-

ted to offer to the public wide ranging SNP analyses

providing information on their ancestry, and pre-

dispositions to possible diseases (see, for example,

https://www .23andme.com/ or http://www.dec ode.com/).

Although their approach is controversial and not

forensically oriented, it is a good example of the

power of the SNP analysis technologies. Applications

of SNPs in context of forensic intelligence will

be brieﬂy mentioned later.

Forensic DNA Evidence. Figure 2 Figure from [1] showing the result of an analysis performed on an individual with

the SGM plus hit. The raw data are decomposed by color: the labels below the peaks show the designation of the

detected alleles. She name above is the STR name. For most STRs, our individual has two peaks and is heterozygote

for these makers. For VWA, this person precents only one peak and is therefore homozygote for that particular marker.

576

Forensic DNA Evidence

DNA Sequencing

This method consists in reading the sequence of the

nucleotides of small pieces of DNA. It is the standard

tool for mtDNA analysis . More recent ‘‘whole genome

DNA sequencing’’ technologies are being developed.

They are massively paralle l sequen cing approaches

with the potential to provide the complete sequence

of an individual in a single process. Their potential for

forensic DNA analysis is not yet clear.

DNA used as Evidence and

Interpretation

DNA (human, animal or vegetal) can be used in diverse

areas: nature and species preservation, food control, miss-

ing persons, mass disaster identiﬁcation, serious, and

volume crime. As parents transmit part of their DNA to

their children, parentage testing using DNA (autosomal

and nonautosomal) is also common, whether for civil

cases, historical cases (e.g., Thomas Jefferson, Nicolas

II), immigration, or genealogy. DNA techniques are very

sensitive and sources of DNA are diverse (e.g., blood,

saliva,sperm,dandruff,skin,hair(nuclearDNAifroot,

mtDNA on shaft, bones, teeth...), which explains the

great potential of forensic DNA analysis.

DNA evidence can help the court in assessing three

types of propositions [5]: offence level propositions

(e.g., the suspect has raped the victim vs. the suspect

has not raped the victim), activity level propositions

(e.g., the suspect has had sexual intercourse with the

victim vs. the suspect has not had sexual intercourse

with the victim) and source level propositions (e.g., the

recovered DNA comes from the suspect vs. the recov-

ered DNA originates from a person unrelated to the

suspect). The higher the hierarchy (from source to

offence level), the more information will be required

to inform an opinion. Through DNA proﬁling and

other means, the forensic scientist is usually only able

to provide useful evidence for source and activity

levels. If addressing source level proposition, the scien-

tist will take into account the rarity of the DNA proﬁle,

estimating the match probability (Weir and Evett), [6].

When addressing activity level propositions, the foren-

sic scientist will in addition take into account transfer

and persistence of DNA (or/and blood pattern in the

presence of blood, see [7]), as well as the relevance of

the trace to the alleged activities.

DNA interpretation is a very large subject area [8, 6,

9–11] and (NRC reports I and II). With the large

number of polymorphisms available, DNA of an indi-

vidual can certainly be considered as unique. Thus,

DNA proﬁles are frequently viewed as unique in the

general public, but they are not. Only a limited number

of polymorphisms are examined in DNA proﬁling,

providing DNA proﬁles that are indeed very rare, with

match probabilities smaller than 1 in a billion. The value

of DNA evidence is usually assessed using the likelihood

ratio approach (also called the Bayesian approach). The

evidence is evaluated considering two propositions (e.g.,

the prosecutor’s and the defence’s): in the given example,

the forensic scientist would, for example, assess the

probability of the evidence given that the suspect has

had sexual intercourse with the victim and the probabil-

ity of the evidence given that the suspect denies knowing

the victim. This approach insures an unbiased interpre-

tation of the evidence.

DNA Used as an Intelligence Tool

With the launching of DNA databases in the 1990s,

DNA has become a very useful intelligence tool. Most

countries have national DNA databases or are in the

process of doing so. The largest are the USA database

and the England and Wales DNA database. Each coun-

try has its own legislation and own set of STR loci (in

Europe there is a set a ‘‘core’’ loci that are used by all

EU countries). The most common program used for

storing and searching the DNA proﬁles is CODIS

(Combined DNA Index System). The program was

developed by the FBI and the private ﬁrm SAIC. The

proﬁles are stored in different indexes (e.g., forensic

proﬁles index, offender index, victim index, staff

index, and missing person’s relatives index). This

allows comparing only proﬁles that should be (e.g.,

the proﬁles from relatives of missing persons will not

be compared to crime scene proﬁles). Criteria for

entering a proﬁle in a database var y according to the

country and the size of the database. DNA databases

rely on the fact that the vast majority of crimes is

committed by a small proportion of the population,

that tends to re offend and on the fact that DNA

proﬁles are extremely rare. This last prerequisite is

not fulﬁlled with so-called partial DNA proﬁles (i.e.,

does not present results for all loci in the given kit

because of DNA degradation), or with mixture DNA

Forensic DNA Evidence

577

Forensic DNA Evidence. Table 1 From [1] Table showing an example of multiplex kits available. Highlighted in dark gray are the markers chosen by the European

Network of Forensic Science Institutes to warrant compatability across countries; in light and dark gray the markers chosen for the USA combined DNA Index System

(CODIS) database

Supplier ABI ABI ABI ABI ABI ABI Promega Promega Promega Promega Serac Serac Biotype

Kit Name Cofiler Profiler

Profiler

Plus

SGM

Plus Identifiler Sefiler Powerplex 1 Powerplex 2 Powerplex 16 Powerplex ES MPX2 MPX3

Mentype

Nonaplex

Marker

THO1 x x x x x x x x x x x x

VWA x X x x x x x x x x x x

D21S11 X x x x x x x x x x

FGA x X x x x x x x x x x

D8S1179 X x x x x x x x x x

D18S51 x x x x x x x x x x

D3S1358 x x x x x x x x x x x x

TPOX x x x x x x x

CSF1PO x x x x x

D13S317 x x x x x

D7S820 x x x x x x

D5S818 x x x x x x

D16S539 x x x x x x x

D2S1338 x x x x

D19S433 x x x x

Penta-D x

Penta-E xx

SE33 x x x x

578

Forensic DNA Evidence

proﬁles. That type of DNA proﬁles has to be used with

more caution in conjunction of the database, especial-

ly, if the suspect population is large (i.e., the searched

database is large). When there is no other forensic

evidence than DNA to limit the suspect population,

then the discriminating power of the technique must

be higher, than if there are other means (e.g., partial

ﬁngerprints, modus operandi, micro-traces, and tradi-

tional police investigation information).

New approaches of the DNA database involve

the use of partial proﬁles and familial searching for

intelligence purpose. In general, to limit adventitious

matches, partial proﬁles with less than six loci, fo r

example, are generally not entered in the database,

but they could be used to generate intelligence. Familial

searching aims at helping the investigation when

no match is found in the database. The technique con-

sists in looking for proﬁles that share alleles with the

crime scene proﬁle. As it is more common for relatives

to share part of their DNA than unrelated persons, there

are examples where it was possible to ﬁnd in the data-

base a close relative of the offender. The Forensic Science

Service (UK) has been able to solve a couple of famous

cases using this method. There are ethical issues to

consider when using this technique [12].

The analysis of some SNPs can predict physical

characters (such as red hair, eye colour, ...) based on

the analysis of the crime scene sample (see www.

dnaprint.com).

Conclusion

The advent of DNA analysis and DNA databases has

revolutionised forensic science, police investigation

and the whole criminal justice system. It is anticipated

that automation will play tomorrow an even more

important role than today. With the advent of ultra-

sensitive methods, the relevance of the recovered

material, the questions of transfer and persistence

of DNA will become the core of interpretation.

Today, the research in this area is still scarce and

needs to be developed. Regarding the techniques, anal-

ysis of STR is here to stay for years. Other fascinating

techniques for SNP analysis or even whole genome

sequencing are coming. But they will not improve

much the performance of DNA proﬁling and their

use will require very difﬁcult validations before they

can diffuse widely into the routine practice. As it was

portrayed in the ﬁlm ‘‘Gattaca’’ by Mike Nichols, 1997,

it seems clear that DNA on a chip and DNA as a

biometric system at the ﬁnger tip will be available

one day. But that day is not yet at the horizon.

Related Entries

▶ LCN DNA/Low Template Level

References

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