10/2/2019

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Sexual Assault Kit Processing

Jason L. Linder

Nebraska State Patrol Crime Lab

Locard’s Exchange Principle

“The microscopic debris that covers our bodies are the mute witnesses, sure and faithful, of all movements and all our encounters.”

-Edmond Locard

1930 Edmond Locard

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Biology

• Serology– Screening Tests

– Diagnostic Tests

– Characterization tests

• DNA– PCR

– STRs

– DNA Databank/CODIS

SAK Approach

• Start with most intimate and move out– Use of case synopsis

– Kit forms• Last sexual activity

• Reported assault type

• Condoms

– Body swabs• Why are you collecting?

– Touch vs. saliva?

– Swab box labeling

Serology

• Screening Tests – Semen

– Alternate Light Source

• Alternate Light Source

• Semen

• Other Body Fluids

• Hairs and Fibers

– IR Camera

• Blood on dark fabrics

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Serology

yogurt

semen

urine

salivalotionmilk

glue

Serology

Luminol Leucomalachite Green

Acid Phosphatase

Serology

• Diagnostic Testing

– Confirmation of Blood

• HemaTrace card– Human Hemoglobin

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Serology

• Diagnostic Testing

– Confirmation of Semen• Microscopic Examination

– Christmas Tree Stain

» Nuclear Fast Red

» PicroidigocarmineGreen

• Seratec Card– Immunodiffusion test for

Prostate Specific Antigen

Y-Screen

• Dirty extraction to test for presence of male DNA

– More sensitive

– Batch cases

DNA

• What is DNA– Deoxyribonucleic Acid

– Genetic blue print for life

• Benefits– Unique to each person,

except for identical twins

– DNA is the same throughout the body

– DNA is highly stable

– Testing is highly sensitive

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Where Can I Use It?

• Homicide

• Sexual Assault

• Assault

• Property Crimes

• Missing Persons

• Paternity

• Burglary/Robbery

• Virtually any case

Types of Evidence Encountered

• Blood

• Semen

• Saliva

• Skin/Tissue

• Bone

• Hair

• Touch (skin cells)

History

• DNA in Forensics

– “DNA Fingerprinting” described by Dr. Alec Jeffreys in 1985

– First use in a case – 1986 in England• Double rape/homicide of two you girls

– False confession

– DNA roundup

» >4,000 males tested – No match

» Colin Pithfork had a friend give his sample

• Tested and matched semen from both scenes

• Convicted and sentenced to life

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DNA

• nDNA

– Found in the Cell Nucleus

– Packaged as Chromosomes

– Double Stranded

DNA

• 46 Chromosomes (23 Pair)

–23 From Mom

–23 From Dad

DNA

• 23 Pairs (46 Total) of chromosomes

• Locations on a chromosome are defined as genes or loci

– 24 Loci (21 + 3 Sex Typing)

• GlobalFiler Kit

• Variations within a locus are called alleles– STR (Short Tandem Repeats)

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Why Use DNA?

• Sensitivity• Specificity (Power of Discrimination)• Stability• Reliability – Gold Standard• It’s Cool – Jury's expect it

Why Use DNA?

• Stable– Naturally protected

– Case >40 years old

• Degradation– Heat

– Humidity

– UV

– Mold growth

Why Use DNA?

• Sensitivity– There is approximately 7 pg of DNA in a cell

– Our target range is 1 ng of DNA• This is approximately 143 cells (~286 sperm cells)

• One drop of blood contains about 10-20 thousand white blood cells

– Theoretically: 1 cell will give a (partial) DNA profile

(1 gram = 1 trillion pg = 1 billion ng)

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DNA Concerns

• Sensitivity and Contamination– Sources

• Law Enforcement

• Medical Personnel

• Crime Lab Analysts

• Anyone or anything in contact with the evidence

– Prevention• Gloves/Masks/Etc

• Package items individually

• Avoid talking/coughing, etc around evidence

DNA Processing

The Lab Work

DNA Analysis

• Evidence Screening

– Documentation of evidence

• Packaging, description, condition, etc.

– Presumptive Testing

• Blood, Semen, Saliva, & Urine

– Confirmatory Testing

• Blood & Semen

– Sample Collection

• Stain selection, touch DNA collection

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DNA Analysis

• DNA Extraction

Differential Extraction

Victim Suspect

1A1A E Included Excluded

1A S Excluded Included

DNA Analysis

• DNA Quantitation

– How much usable human DNA is in the sample?

– Quant stop value: No further processing

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DNA Analysis

• PCR (Polymerase Chain Reaction)

– Molecular “Xerox” machine

– Creates millions of exact copies of the DNA

29 Cycles229 = ~300 Million Copies

DNA Analysis

Genetic Analyzer

DNA Analysis

STRs (Short Tandem Repeats)– Area of DNA with repeating

sequence

– Count the number of repeat units

– Analyze 24 Areas (loci) of DNA• Sex Determining Markers

Reported As:

Locus Person A

TH01 7, 8

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DNA Analysis

DNA Analysis

• Interpretation– Inclusion

• Can be a source of the DNA profile

• Add statistical weight

– Exclusion• Can not be a source of the DNA profile

– No Conclusion or Uninterpretable• Quality or complexity of the DNA profile is not sufficient to

draw a conclusion

Binary Interpretation

Heterozygote Homozygote

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DNA Analysis

Sperm Fraction Victim Suspect

Excluded Included

10,12 8,11 10,12 8,1111,12 8,9

DNA Analysis

Breast Swab Victim Suspect

Included Included10,11,12 8,9,11 10,12 8,1111,12 8,9

Major? Minor?

DNA Analysis

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Two sides to every story

Likelihood Ratios

Hp: The bloodstain came from the person

of interest (POI)

Hd: The bloodstain did not come from the POI. It came from someone

else.

Likelihood Ratios

2.945 Octillion

The DNA Profile from the bloodstain is 2.9 Octillion times more

likely if it had originated from Mr. Suspect than if

it had originated from another unrelated male,

selected at random in the population.

Likelihood Ratio

• 1 Quadrillion = 1,000,000,000,000,000 (15 Zeros)• 1 Quintillion = 1,000,000,000,000,000,000 (18 Zeros)• 1 Sextillion = 1,000,000,000,000,000,000,000 (21 Zeros)• 1 Septillion = 1,000,000,000,000,000,000,000,000 (24 Zeros)• 1 Octillion = 1,000,000,000,000,000,000,000,000,000 (27 Zeros)• 1 Nonillion = 1,000,000,000,000,000,000,000,000,000,000 (30 Zeros)• 1 Decillion = 1,000,000,000,000,000,000,000,000,000,000,000 (33 Zeros)

1 Quadrillion Pennies 1 Quintillion Pennies

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Y-STR Testing

• Y-STR Testing

– Focus on only the Y Chromosome

– Paternally inherited

CODIS

Combined DNA Index System

• Developed in 1998 by the FBI for databankingDNA profiles

• Investigative Tool– Link cases together

– Link cases to convicted offenders

CODIS

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CODIS

• Five Indices– Convicted Offenders

– Forensic Unknowns

– Unidentified Human Remains

– Missing Persons

– Relatives of Missing Persons

Other Technologies

Other Technologies

• Mitochondrial DNA

– May work with cases where nuclear DNA does not

– Maternally inherited

– Primary Use

• Missing Persons/UHRs– UNT Health Science Center

• Hair with no root

– Not performed at the NSP crime lab

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It’s Here

• Forensic Genealogy

– Use of GEDmatch

• Build family trees

– Example Cases

• Golden State Killer

• Alaska Cold Case

– Private Labs

• ~$6,000 per sample

It’s Here, Not Mainstream

Rapid DNASwab in, Profile Out

It’s Here, Not Mainstream

Phenotypic Typing

Physical Traits

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Questions

Thank You Very Much

References

• Butler (2011), Advanced Topics in Forensic DNA Typing: Methodology, San Diego, CA : Academic Press

• Butler (2015), Advanced Topics in Forensic DNA Typing: Interpretation, San Diego, CA: Academic Press

• SWGDAM (2017), Interpretation Guidelines for Autosomal STR Typing by Forensic DNA Testing Laboratories

• SWGDAM (2016), Recommendations for the Efficient DNA Processing of Sexual Assault Evidence Kits in a Laboratory

• SWGDAM (2015), Guidelines for Collection & Serological Examination of Biological Evidence