Sgt. Kevin McKinney

Investigations Division

Elko County Sheriff ’s Office

Uses for DNA in Law Enforcement

Investigations

DNA typing was first described in 1985 by an English Geneticist named Dr. Alec Jeffreys. Dr. Jeffreys developed the ability to perform human identity tests from DNA.

The first court case involving the analysis of DNA was a 1985 English immigration case.

DNA was first used for criminal investigations in the late 1980’s.

History of DNA Use in Law Enforcement

1986: The first criminal case utilizing DNA occurred during a double homicide investigation. Police in England collected 5000 blood samples from men in the community where the homicides occurred and a positive ID was made.

1987: The first criminal conviction involving the use of DNA evidence in the US occurred in Florida on a rape case.

First time that the FBI Forensic Laboratory offered DNA testing for law enforcement was 1989.

Today, every state in the United States has at least one forensic laboratory capable of conducting DNA testing.

History of DNA Use in Law Enforcement

Green River KillerIn early 1980’s several

women were killed in the Seattle, Washington area. At some of the autopsies, semen was collected from the bodies of the victims.

2001, the semen samples were analyzed, DNA was extracted and compared to a reference DNA standard of Gary Ridgway, and Ridgway was positively identified as the source of the semen on 3 of the victims. Ridgway could not be eliminated as the source of the semen on 2 other victims.

Exoneration of Clyde Charles1981: Clyde Charles was

arrested and convicted of Aggravated Sexual Assault in Louisiana and was sentenced to life in prison.

1999: DNA testing on the evidence collected in the Clyde Charles case excluded Clyde Charles as the perpetrator of the sexual assault and he was released from prison.

2000: Clyde’s brother, Marlo was arrested and convicted of the same sexual assault that Clyde was convicted of in 1981 after DNA testing concluded that Marlo was the perpetrator of the crime.

Innocence ProjectChris Ochoa

https://www.youtube.com/watch?v=0xJlsxCGw9w

1989: FBI developed Combined DNA Index System (CODIS) to house DNA profiles of unknown and convicted offenders.

1991: a Minnesota Rape/Homicide was the first case solved through the use of CODIS.

As of August, 2007, CODIS contained over 5 million DNA profiles in its Convicted Offender Index and approximately 188,000 unknown profiles collected from crime scenes.

CODIS

DeoxyriboNucleic AcidPrincipal Component of cellular chromosomes.Responsible for hereditary characteristics in

all life forms.Double helix designComposed of 4 nitrogenous bases:

AdenineGuanineCytosineThymine

DNA

Human cell contains 46 chromosomes which have a DNA structure built from randomly alternating base pairs of nucleotide arrangements.

Combinations of nucleotide arrangements are almost infinite.

Vast majority of nucleotides are commonly shared by all human beings. 99.5% similar

Small portion of nucleotides is sufficiently unique and variable in base pairings sequence to discriminate one individual from another individual. Regional or Ethnic differences

DNA

Restriction Sites: Nucleotide combinations (RFLPs) repeat themselves in random intervals throughout the length of the DNA chain.

Extraction: DNA is extracted from biological sample.

Amplification: The DNA chain is broken down chemically at restriction sites and copied.

Sequencing: The DNA chain is then sequenced to find the “bar code” or banding pattern.

Analysis of DNA

The basic use of DNA in law enforcement is for identification.Identify VictimsIdentify SuspectsEliminate SuspectsIdentify Persons at a Crime Scene

Investigative Uses of DNA

BloodSemenSalivaTissueBonesTeeth

Hair Nails“Touch DNA”

Types of Evidence that contain DNA

The difficulty with DNA in investigations is not the collection of crime scene or unknown DNA samples, but with being able to match the unknown DNA samples with individuals.

The DNA samples must be compared to known samples for a positive identification.

Investigative Uses of DNA

DNA is used to identify victims, often death victims, who have decomposed to the point that facial recognition or fingerprint comparison cannot be used.

DNA collected from a victim is most often compared to probable family members (parents, siblings, children) for identification.

Identifying Victims

Death Victim DNA

DNA evidence can be used to either positively identify or eliminate a potential suspect as being the perpetrator of the crime.

Typically, a reference standard is collected from a potential suspect that is then compared to DNA evidence found on a victim or at a crime scene.

Occasionally transfer DNA evidence can be found on a suspect and collected, which is then compared to the victim’s DNA.

Identifying Suspects

DNA evidence is collected at a crime scene to identify persons who were present at the scene, to develop information in regards to potential victims, witnesses and/or suspects.

The presence of DNA evidence at a crime scene does not positively conclude anything, without further investigation.

Crime Scene DNA

Crime Scene DNA

Crime Scene DNA

Crime Scene DNA

DNA evidence is collected through the collection of evidence items that have biological DNA evidence on/in it or through swabbing the area of the item that the biological DNA is on/in and then collecting the swabs.

Wet biological DNA samples can be swabbed with a sterile dry swab.

Dry biological DNA samples can be collected with a sterile swab moistened with sterile water.

Items containing DNA must be completely dried and then kept in a sealed breathable (paper) package to inhibit degradation of the sample.

DNA samples are sent to the Forensic Lab for analysis.

DNA Collection

STR: The standard type of testing used for analyzing DNA samples

Mitochondrial: Used for analyzing DNA samples that are highly degraded or from DNA samples that come from bone teeth or hair.

Types of DNA Analysis

4 potential results:DNA examination positively identifies an

individual as being the source of the DNA sample.

DNA examination excludes an individual as being the source of the DNA sample.

DNA examination reveals mixed DNA samples that neither identifies or excludes an individual as being the source of the DNA sample

DNA sample is insufficient for examination and comparison.

Results of DNA examinations

Thank You

Questions?