Decision-Makers: Judges and Juries

CS593: Digital Forensics — D. Kevin McGrath

• Decision-Makers: Judges and Juries
  • Overview
  • Judges
    • How Judges Are Chosen: Election vs. Appointment
    • What Judges Do
  • Scientific Evidence
    • The Gold Standard: DNA
    • Pattern Identification Disciplines
    • Where Does Digital Forensics Fit In?
  • Juries
  • Jury Selection
    • Jury Pools
    • Voir Dire
  • Juror Comprehension
    • Juror Background
    • Racial Biases
    • Comprehension Ability
  • Jury Deliberations
  • What Determines the Outcome of Cases?

Overview

The two kinds of decision-makers in litigation are judges (who decide what evidence is admitted) and juries (who evaluate evidence to reach verdicts). Both civil and criminal cases require both sides to develop and exchange evidence before trial — a process called discovery. This lecture examines how decision-makers are chosen, how they process evidence, and what determines case outcomes.

An important framing note: in a criminal system, the verdict is either “guilty” or “not guilty” — not guilty or innocent. Being acquitted only means the prosecution failed to meet its burden of proof. You can be acquitted and still have done it; you can be convicted without having been near the crime.

Judges

Judges make decisions about what evidence is included in a case and whether expert testimony is admissible. Most are lawyers and members of the local bar — socially similar to the attorneys who appear before them.

Judges are also bureaucrats: they are under pressure to dispose of caseloads efficiently, avoid reversals by higher courts, and keep proceedings moving. Doing justice may not always be their first priority.

How Judges Are Chosen: Election vs. Appointment

Elected judges:

• Elections are usually nonpartisan and extremely low-profile.
• Theory: judges are accountable to their communities.
• Problem: political pressure. Elected judges in states with the death penalty almost never vote against imposition of the death penalty, even in cases with clear misconduct. (Louisiana example: no state Supreme Court justice has ever voted against a death sentence.)

Appointed judges:

• Federal system: President nominates, Senate confirms; federal judges receive lifetime appointments.
• Theory: insulated from direct political pressure; free to follow the law wherever it leads.
• Problem: also insulates them from common sense; lifetime appointments can protect corruption and incompetence.

Neither system is clearly superior — each involves trade-offs.

What Judges Do

From a DF perspective, the most important judicial function is making decisions about admitting evidence. Judges must decide:

• Whether evidence is relevant to the proceeding.
• Whether the expert’s qualifications are sufficient.
• Whether expert evidence is reliable and valid — how scientific it is, and how scientific it needs to be.

Ironically, these determinations about the scientificity of evidence are made by people who are often lawyers precisely because they were bad at science.

Scientific Evidence

Scientific and technical evidence carries enormous weight with jurors — jargon impresses them even when they don’t understand it. Courts became concerned about “junk science” (notably tobacco industry studies claiming smoking was harmless) and the Supreme Court articulated standards for admission of scientific evidence through the Daubert Trilogy.

The Gold Standard: DNA

DNA evidence is the gold standard of forensic science because it:

• Originated outside the criminal justice system — developed by scientists for dating bones, establishing paternity, etc. It is real science with uses beyond law enforcement.
• Has generally accepted protocols for collection, handling, and quality assessment.
• Has fully developed standards for making identifications and ruling out alternative donors.
• Quantifies error rates probabilistically: “There is a 1 in 100,000 chance this sample did not come from the defendant.” Experts explicitly acknowledge the possibility of error.

Pattern Identification Disciplines

Pattern identification disciplines — fingerprints, hair analysis, ballistics, tool marks, handwriting analysis — compare samples from a crime scene to samples from a suspect. These disciplines:

• Emerged from the needs of law enforcement, not from science. They have no applications outside criminal justice.
• Lack an empirical basis: the proposition that all fingerprints are unique has never been empirically established.
• Suffer from cognitive bias: analysts who work for labs that report exclusively to police are more likely to call a match.
• Cannot quantify error rates in a meaningful way — for years, fingerprint analysts testified to 100% certainty.

Hair microscopy example: The FBI used hair microscopy for decades. After the Innocence Project requested reexamination of ~2,000 cases, DNA testing of the hair evidence showed an error rate of at least 90% — and every error favored the prosecution (FBI 2015). Pattern identification disciplines are in danger of being reclassified as junk science.

Where Does Digital Forensics Fit In?

Digital forensics has a relatively limited scientific basis. Many techniques were developed on an ad hoc basis because they seemed to work, without establishing scientific foundations. Key questions DF must answer to be taken seriously:

• Is there an empirical basis for conclusions?
• Can error rates be demonstrated and discussed?
• Are techniques accepted by the scientific community?
• Is there peer review and a research culture?

The DF community needs to be more thoughtful about limiting law enforcement’s role in shaping the discipline.

Juries

Juries are a feature peculiar to Anglo-American (and Korean) legal systems — popular in adversarial systems, unusual in inquisitorial ones.

Petit juries hear cases and deliver verdicts. Grand juries exercise oversight over prosecutors. As an expert witness, you will be addressing petit juries.

Juries represent a unique form of political participation: a chance to make decisions about how your community allocates justice.

Jury Selection

Jury selection is a two-stage process.

Jury Pools

Jurors are summoned from jury pools assembled from public records. Originally built from voter registration rolls (skewing white and middle-class), most jurisdictions now use driver’s license records, which provide better demographic representation. However, bias by race and class persists.

Voir Dire

Voir dire (French: “to see, to speak”) is the process by which attorneys question potential jurors to identify biases. Jurors are removed by two mechanisms:

• Challenge for cause: A juror is removed if they have a specific conflict of interest (know a party, work for an insurance company, have too much prior knowledge of the case). Attorneys are allowed an unlimited number of challenges for cause.
• Peremptory challenge: A juror is removed without stated reason; each side receives a limited number. Peremptory challenges are sometimes used illegally to exclude minority jurors — cases where this is alleged are called Batson cases. Courts have been inconsistent in enforcing the prohibition.

Following voir dire, the jury is supposed to be free of obvious bias.

Juror Comprehension

Jurors are active information processors — they fit evidence into their existing stories of what happened, filtered through their values, life experiences, and preconceptions.

Juror Background

• Educational background affects how jurors process complex evidence.
• Cases involving digital forensics may actively seek jurors with technical backgrounds during voir dire.
• Pre-existing attitudes shape how jurors respond to witnesses — evidence that conflicts with preconceptions may be discounted.

Racial Biases

Racial bias in jury decision-making is real but complex:

• There is some evidence of cross-racial bias (whites voting against blacks and vice versa).
• However, authoritarian personalities tend to be harsher toward defendants of their own race.
• White jurors motivated to avoid appearing racist will often render color-blind verdicts when race is salient in the trial — but are more likely to express bias when race is not salient and there is a convenient pretext.

Comprehension Ability

• Jurors do a good job comprehending ordinary evidence; they collectively remember a great deal, with different jurors attending to different parts of testimony.
• Jurors are poor at comprehending scientific or technical evidence. They tend to defer to whichever “scientific” expert is on the stand — and since most defendants can’t afford experts, that expert is typically the prosecution’s.
• Jury instructions are notoriously incomprehensible (written by lawyers, in dense prose without punctuation). Some courts do not even let jurors take notes.

Jury Deliberations

Jury deliberations are “black boxes.” The Supreme Court has ruled that even if jurors are drunk, snorting cocaine, and falling asleep during a trial, their verdicts cannot be disturbed — disturbing one verdict would open a slippery slope.

What is known:

• Jurors receive jury instructions before deliberating — a statement of the applicable law. Instructions are poorly understood.
• Juries tend to focus on evidence, not on abstract opinions about what should happen.
• Jurors pool their memories: the jury as a body remembers far more than any individual.
• Juries struggle more with instructions even after deliberating.

What Determines the Outcome of Cases?

Four major factors (Eisenstein and Jacob 1977):

1. Law and evidence (including digital forensics evidence). Important, but only one of several factors.
2. Characteristics of judges: race, gender, ideology have some effect; comfort with technology and science has an especially significant effect on how judges handle digital evidence.
3. Characteristics of defendants and victims: race and resources are the most important. The race of the victim matters more than the race of the defendant — crimes against white victims are prosecuted more aggressively, result in more convictions, and yield harsher sentences. Most criminal defendants are poor and people of color.
4. Characteristics of court processes: different courts (and different clerks) have dramatically different attitudes about how cases proceed. Even the county clerk can tell you to go away and mean it.