nij_DNA_Evidence.pdf

Where can DNA evidence be found at a

Evidence Collection and

Preservation

DNA evidence can be collected from virtually anywhere. DNA

has helped solve many cases when imaginative investigators

collected evidence from nontraditional sources (see “Identifying

DNA Evidence”). One murder was solved when the suspect’s

DNA, taken from saliva in a dental impression mold, matched

the DNA swabbed from a bite mark on the victim. A masked

rapist was convicted of forced oral copulation when his victim’s

DNA matched DNA swabbed from the suspect’s penis 6 hours

after the offense. Numerous cases have been solved by DNA

analysis of saliva on cigarette butts, postage stamps, and the

area around the mouth opening on ski masks. DNA analysis of

a single hair (without the root) found deep in the victim’s throat

provided a critical piece of evidence used in a capital murder

Investigators and laboratory personnel should work together to

determine the most probative pieces of evidence and to establish

priorities. Although this brochure is not intended as a manual for

DNA evidence collection, every officer should be aware of

important issues involved in the identification, collection, trans-

portation, and storage of DNA evidence. These issues are as

important for the first responding patrol officer as they are for the

experienced detective and the crime scene specialist. Biological

material may contain hazardous pathogens such as the human

immunodeficiency virus (HIV) and the hepatitis B virus that can

cause potentially lethal diseases. Given the sensitive nature of

DNA evidence, officers should always contact their laboratory

personnel or evidence collection technicians when collection

questions arise.

Identifying DNA Evidence

Fingerprints

DNA Strands

Since only a few cells can be sufficient to obtain useful DNA information to help your case, the list below

identifies some common items of evidence that you may need to collect, the possible location of the DNA on

the evidence, and the biological source containing the cells. Remember that just because you cannot see a stain

does not mean there are not enough cells for DNA typing. Further, DNA does more than just identify the source

of the sample; it can place a known individual at a crime scene, in a home, or in a room where the suspect

claimed not to have been. It can refute a claim of self-defense and put a weapon in the suspect’s hand. It can

change a story from an alibi to one of consent. The more officers know how to use DNA, the more powerful

Possible Location of

Source of DNA

DNA on the Evidence

baseball bat or similar weapon

handle, end

sweat, skin, blood, tissue

inside

sweat, hair, dandruff

nose or ear pieces, lens

sweat, skin

facial tissue, cotton swab

surface area

mucus, blood, sweat, semen, ear wax

surface area

blood, sweat, semen

tips

saliva

cigarette butt

saliva

licked area

saliva

inside/outside surface

skin, sweat

sides, mouthpiece

saliva, sweat

inside/outside surface

semen, vaginal or rectal cells

surface area

sweat, hair, semen, urine, saliva

“through and through” bullet

outside surface

blood, tissue

person’s skin or clothing

saliva

fingernail, partial fingernail

scrapings

blood, sweat, tissue

Where can DNA evidence be found at a

crime scene?

Evidence Collection and

Preservation

DNA evidence can be collected from virtually anywhere. DNA

has helped solve many cases when imaginative investigators

collected evidence from nontraditional sources (see “Identifying

DNA Evidence”). One murder was solved when the suspect’s

DNA, taken from saliva in a dental impression mold, matched

the DNA swabbed from a bite mark on the victim. A masked

rapist was convicted of forced oral copulation when his victim’s

DNA matched DNA swabbed from the suspect’s penis 6 hours

after the offense. Numerous cases have been solved by DNA

analysis of saliva on cigarette butts, postage stamps, and the

area around the mouth opening on ski masks. DNA analysis of

a single hair (without the root) found deep in the victim’s throat

provided a critical piece of evidence used in a capital murder

Investigators and laboratory personnel should work together to

determine the most probative pieces of evidence and to establish

priorities. Although this brochure is not intended as a manual for

DNA evidence collection, every officer should be aware of

important issues involved in the identification, collection, trans-

portation, and storage of DNA evidence. These issues are as

important for the first responding patrol officer as they are for the

experienced detective and the crime scene specialist. Biological

material may contain hazardous pathogens such as the human

immunodeficiency virus (HIV) and the hepatitis B virus that can

cause potentially lethal diseases. Given the sensitive nature of

DNA evidence, officers should always contact their laboratory

personnel or evidence collection technicians when collection

questions arise.

Identifying DNA Evidence

Fingerprints

DNA Strands

Since only a few cells can be sufficient to obtain useful DNA information to help your case, the list below

identifies some common items of evidence that you may need to collect, the possible location of the DNA on

the evidence, and the biological source containing the cells. Remember that just because you cannot see a stain

does not mean there are not enough cells for DNA typing. Further, DNA does more than just identify the source

of the sample; it can place a known individual at a crime scene, in a home, or in a room where the suspect

claimed not to have been. It can refute a claim of self-defense and put a weapon in the suspect’s hand. It can

change a story from an alibi to one of consent. The more officers know how to use DNA, the more powerful

Possible Location of

Source of DNA

DNA on the Evidence

baseball bat or similar weapon

handle, end

sweat, skin, blood, tissue

hat, bandanna, or mask

inside

sweat, hair, dandruff

nose or ear pieces, lens

sweat, skin

facial tissue, cotton swab

surface area

mucus, blood, sweat, semen, ear wax

surface area

blood, sweat, semen

tips

saliva

cigarette butt

saliva

stamp or envelope

licked area

saliva

inside/outside surface

skin, sweat

bottle, can, or glass

sides, mouthpiece

saliva, sweat

inside/outside surface

semen, vaginal or rectal cells

blanket, pillow, sheet

surface area

sweat, hair, semen, urine, saliva

“through and through” bullet

outside surface

blood, tissue

person’s skin or clothing

saliva

fingernail, partial fingernail

scrapings

blood, sweat, tissue

Elimination samples

As with fingerprints, the effective use of DNA may require the

collection and analysis of elimination samples. It often is neces-

sary to use elimination samples to determine whether the evi-

dence comes from the suspect or from someone else. An officer

must think ahead to the time of trial and possible defenses while

still at the crime scene. For example, in the case of a residential

burglary where the suspect may have drunk a glass of water at

the crime scene, an officer should identify appropriate people,

such as household members, for future elimination sample test-

ing. These samples may be needed for comparison with the saliva

found on the glass to determine whether the saliva is valuable

evidence. In homicide cases, be sure to collect the victim’s DNA

from the medical examiner at the autopsy, even if the body is

badly decomposed. This may serve to identify an unknown victim

or distinguish between the victim’s DNA and other DNA found at

When investigating rape cases, it may be necessary to collect and

analyze the DNA of the victim’s recent consensual partners, if

any, to eliminate them as potential contributors of DNA suspect-

ed to be from the perpetrator. If this is necessary, it is important to

approach the victim with extreme sensitivity and provide a full

explanation of why the request is being made. When possible,

the help of a qualified victim advocate should be enlisted for

COmbined DNA Index System—

CODIS (COmbined DNA Index System), an electronic database

of DNA profiles that can identify suspects, is similar to the AFIS

(Automated Fingerprint Identification System) database. Every

State in the Nation is in the process of implementing a DNA

index of individuals convicted of certain crimes, such as rape,

murder, and child abuse. Upon conviction and sample analysis,

perpetrators’ DNA profiles are entered into the DNA database.

Just as fingerprints found at a crime scene can be run through

AFIS in search of a suspect or link to another crime scene,

DNA profiles from a crime scene can be entered into CODIS.

Therefore, law enforcement officers have the ability to identify

possible suspects when no prior suspect existed.

What Every Law

Enforcement

Officer Should

Know About

DNA

Evidence