Role and Impact of Forensic Evidence in the Criminal Justice Process

Role and Impact of Forensic Evidence
in the Criminal Justice Process
Justice Research and Statistics Association
October 23, 2009
Joseph Peterson, Ira Sommers,
Donald Johnson, Deborah Baskin
School of Criminal Justice and Criminalistics
California State University, L A
Los Angeles, CA

Background
Forensic sciences have seen dramatic
scientific breakthroughs in last 25 years
The CSI phenomenon has sensitized CJ
personnel and public to forensic science
Still, lab resources have not kept pace
with submissions and backlogs >500K
Many federal efforts (DNA Initiative,
Coverdell Act, etc.) have assisted

Background (continued)
Many professional programs have evolved to
elevate quality of forensic lab results
Still, scandals have shaken crime lab profession
(FBI, West Virginia, Houston PD, etc), causing
concern over reliability of evidence
U.S. Supreme Court decisions (Daubert, etc.)
have named judges as ‘gatekeepers’ to assess
quality and reliability of scientific evidence
National Academy of Sciences panel issued
landmark critical report in February 2009

National Institute of Justice
Research Solicitation
It has been 25 years since there was an
assessment of the uses and effects of
scientific evidence on police and courts
An estimated $1.5 billion is spent annually
on forensic services but question remains:
What are its uses and impact?
NIJ solicited proposals in 2006 to assess
the role and impact of forensic services

NIJ Project Goals
Determine:
Percent of crime scenes with forensic evidence
Varieties of forensic evidence recovered from
different categories of major crimes
Track evidence collection, analysis and attrition
of evidence from incident thru lab into courts
Identify types of forensic evidence that
contribute most often to successful case
outcomes (relative to its availability)

Prevalence of Crime Labs and
Scientific Evidence
Presently are about 400 crime laboratories
nationwide examining 2.5 M requests annually
Studies in 1980s found evidence collected in
only about 20-30% of cases, varying greatly by
offense type
Huge investment in DNA over past five years
Controlled substances (70%) still dominate lab
caseloads, followed by biological evidence,
firearms and fingerprints

Present NIJ Study
Thirty (30) month project Oct 06-Apr 09
Three study sites selected representing city,
county, and state-wide laboratory systems:
Los Angeles County, CA
Indianapolis, IN
Indiana State Police Lab and local jurisdictions of
South Bend, Ft. Wayne, and Evansville

Data Collection
Prospective analysis of (2003) official records,
data tracking police incidents (into/out of
laboratory) to final case disposition
Stratified, random sample (homicides, agg.
assaults, rapes, robberies, & burglaries) of
more than 4,000 incidents selected from
police files in each of five study sites
Police incident, crime scene, investigator,
laboratory, prosecutor, and court files
reviewed

Critical Decision Points
Crime scene evidence collection
Laboratory acceptance, prioritization and
analysis (criminalist, detective, prosecutor)
Police decision to investigate, arrest and/or
exclude suspects
Prosecutor decision to file charges, accept
pleas, or take cases to trial
Fact-finders/pros and defense attorneys use
of scientific evidence, reports and testimony

Independent Variables
Key Individual Case-Level
Demographics of suspect/victim, offense type,
report/response time, witnesses,
information/evidence collected, scientific
results, offender and case processing
characteristics, key decisions, demographics

Key Dependent Variables
Logistic Regression Analysis
If reported crime led to arrest
If arrest referred to prosecutor
If prosecutor filed charges
Manner of disposition (plea/trial)
Convict/no convict
If convicted, nature of sentence
Length of sentence

Incidents Randomly Sampled
by Jurisdiction (2003*)
LA IN EV FW SB
HOM 245 71 14 38 32
RAPE 231 150 75 70 76
ROBB 528 335 80 73 65
ASSLT 230 323 108 95 103
BURG 489 350 142 144 138

Per Cent Offenses with Crime
Evidence Collected
LA(%) IN(%) EV(%) FW(%) SB(%)
HOM 96 97 100 100 100
RAPE 51 73 75 66 72
ROBB 19 28 44 25 35
ASSLT 25 33 26 38 32
BURG 21 23 15 15 16

Phys Evid/Substrates Collected
Indianapolis Crime Scenes
HOM
(%)
RAPE
(%)
ROBB
(%)
ASSLT
(%)
Biolog 89 63 0.3 5.3 2
Prints 75 2 16 0.3 20
BURG
(%)
Firearms
Nat/Syn
Matrls
82 0.7 7 26 0
69 47 0.9 0.3 0.3

Moderate Filtering of Forensic
Evidence in Los Angeles
CLLCT
SCENE
SBMIT
LAB
HOM RAPE ASSLT ROBB BURG
(%) (%) (%) (%) (%)
96 51 25 19 21
92 49 13 8 19
EXAM 80 22 7 7 10

Major Filtering of Evidence in
CLLCT
SCENE
SBMIT
LAB
HOM
(%)
Evansville
RAPE
(%)
ASSLT
(%)
ROBB
(%)
100 75 26 44 15
100 11 8 13 3
EXAM 100 11 8 13 3
BURG
(%)

Crime Lab Results (Indianapolis)
EXAM
(#)
INDIV
(#)
+ID
(#)
-ID
(#)
HOM 55/56 31 4 8 0
RAPE 25/44 6 11 0 0
ROBB 43/44 32 36 0 0
HITS
(#)
ASSLT 33/39 14 10 0 1 AFIS
BURG 47/47 35 36 0 4 AFIS

BiVariate Relationships
Cases With/Without Forensic Evidence
Collected, Submitted, and Examined
Arrest
Referral
Charge
Outcome
Sentence

Arrests Rates for Offenses With
and Without Crime Scene Evidence
LA(%) IN(%) EV(%) FW(%) SB(%)
HOM* 46/40 73/100 100/0 47/0 78/0
RAPE 56/50 78/44 25/11 22/8 29/5
ROBB 50/19 45/9 63/16 44/7 35/5
ASSLT 51/71 73/37 75/36 58/20 39/24
BURG 13/9 12/5 29/6 24/6 9/6

Bivariate Relationships: Crime Scene
Evidence (Y/N) and Case Progress
(Number of Sites Where Significant*)
HOM ASSLT RAPE ROBB BURG
ARRST * *** ** ***** ***
REFRL * * NS * NS
CHRG
E
NS * NS ** NS

Cases with Crime Scene Evidence
as Significant Predictor of Arrest
Los Angeles - Homicide*, Robbery
Indianapolis - Rape, Assault, Robb, Burg
Evansville - Assault, Robbery, Burglary
Fort Wayne - Assault and Robbery
South Bend - Rape and Robbery
*Firearms, Materials Evidence

Cases Where Crime Scene Evidence
Significant Predictor of Arrest -
Fraction Examined Prior to Arrests
ASSLT RAPE ROBB BURG
LA 2/131
INDY 7/158 13/103 9/62 2/23
EVANS 1/50 6/29 1/13
FW 0/33 4/12
SB 1/17 0/10

Explaining Higher Arrest Rates For Cases
with For. Evidence, But Not Yet Examined
Are these cases different in fundamental
ways?
How/who reports them
How suspects are identified/apprehended
Relationship between victim and suspect
Does physical evidence have immediate value even
though not yet examined?
Is quantum of proof for an arrest satisfied with
presumptive scientific evidence?

Role of Forensic Evidence in
Direct vs. Descriptive Arrests
Hypothesis: Forensic evidence of greater
value in direct observation cases
Direct:
Suspect apprehended, admission, suspect
surrender, arrest in another case, police observe,
traffic stop, recovered property
Descriptive:
Vehicular description, citizen observation, photo
ID, suspect description, line-up

Combining Smaller Jurisdictions All
Part of Indiana State Lab System
South Bend
Fort Wayne
Evansville

COMBINED INDIANA SITES: FOR EVID
PREDICTORS OF ARREST (Sig Level***)
HOM ASSLT RAPE ROBB BURG
Crime Scene
Evidence *** ** *** **
Laboratory
* *** ***
Evidence
Lab Examine
Evidence * *** **
Biolog Crime
Scene * **
Prints Crime
Scene ***
Biolog Lab
Evidence * ***
Unique Individuality
*** *

Individualized/Associative Lab
Results, Arrest and Conviction
Total Arrest Convict Rate
Assault 5/859 3 2 67%
Burglary 18/1263 8 4 50%
Hmicide 80/400 57 46 81%
Rape 16/602 11 9 82%
Robbery 14/1081 11 9 82%

Individualized/Associative Evidence
and Conviction Rate
Single Form - 67% (convictions/arrests)
20% firearms
20% biology
57% latent prints
Two or More Forms - 86%
29% biology
29% firearms
14% latents
29% combination of above

Total Individualized Evidence
By Offense
Assault - Bio/Firearms - 5 cases
Burglary - Latent Prints - 18 cases
Homicide - Latents, Firearms, and Bio
80 cases
Rape - Bio/Latents - 16 cases
Robbery - Latents - 14 cases

Plea/Trial and Sentencing
Generally, forensic evidence
strengthens a case and influences cases
to go to trial (Assault, Rape)
Generally, examined forensic evidence
leads to more severe sanctions -
Assault, Burglary (two jurisdictions)

Citizen Polls and Surveys
Field poll (CA) queries of 1201 randomly
selected California registered voters
(telephone) as to their views of reliability and
importance of forensic evidence and:
Television viewing habits
Jury service experience
C J employment
Crime victimization

Citizen Poll Regression Results
Citizens generally perceive forensic evidence
as much more reliable than other forms of
testimonial evidence
Citizens who watch more hours of TV
programming regard forensic evidence as
more reliable
Citizens who watch justice themed TV crime
shows were more than twice as likely to
convict than those who didn’t

Implications for Policy/Practice
Collection of Physical Evidence
Lab Examination of Evidence
Investigations of Crimes
Prosecution and Adjudication
CSI Effect

Investigation for and Collection of
Physical Evidence
Most scenes have physical evidence and much is collected
to insure it does not perish and to comply with modern
forensic science expectations
Much physical evidence is filtered between crime scene and
laboratory analysis - most by crime scene technicians and
detectives
Firearms, latent (finger) prints and biological evidence is
most often collected and submitted
Prosecutors play major role in influencing decisions to
collect, submit and analyze evidence

Criminal Investigations
Physical evidence adds value and momentum to
investigation even before/without lab analysis
Controlling for other investigative factors, forensic
evidence associated with arrest in many cases
Other case characteristics (victim and witness
reports) are also important predictors of arrest
Forensic evidence is valuable at arrest, but less so
at subsequent stages of prosecution/adjudication
Forensic evidence (latent prints and firearms) from
robberies consistently associated with arrest in all
study sites

Laboratory Analysis
Most examinations of evidence will await
determination that results of analysis are
needed
A comparatively small percentage of
examinations result in individuality of
evidence and linkage to suspect/victim
Inquiry into data bases seldom provide
identity of unknown offender

Prosecutions and Adjudications
Prosecutors are very mindful of ‘CSI Effect’
and expectations of court/jurors
Charging decisions are heavily influenced by
overall convictability of case
Value of forensic evidence as predictor
diminishes after charging
Stronger evidence cases, including forensic
evidence, more often result in trial
Sentence/plea bargaining may be influenced
by presence of lab analysis and report

Influence of CSI Effect
Investigators and crime scene technicians very
aware that arrests and prosecutions may not be
sustained unless evidence collected/proper
procedures followed
Prosecutors believe forensic evidence is central
to plea and trial conviction
Prosecutors are pressed to state proper
procedures followed in cases, even those lacking
forensic evidence
Prosecutor view of case needs influences actions
of crime scene, investigators and laboratory

Thank you!