CHAPTER 1 USING FORENSIC EVIDENCE TO PROVE ULTIMATE ISSUES
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Chapter 1 Using Forensic Evidence to Prove Ultimate Issues
What is the nature of forensic evidence? What does it "prove"? How can it be used to prove issues in a criminal trial? Is all forensic evidence "circumstantial"? What role does the law of probability play in forensic evidence? What types of "expert opinions" can forensic experts offer? When should the jury be able to look at the evidence and come to its own conclusions about the meaning of the evidence? Are some types of forensic evidence so powerful that they can unduly sway or "prejudice" a jury? We will examine these questions in detail.
Forensic evidence is any evidence based on science, technique, or expert evaluation entered into evidence at trial. It frequently requires an expert to explain the evidence to the jury. The expert's "opinion" is valuable to the party who presents the expert because it often links the evidence to an issue the jury must decide. The danger that the jury will be unduly impressed by the expert is called the "white coat" effect.
The jury must find all "elements" of a crime by a standard of beyond a reasonable doubt. For the crime of murder, depending on the state or federal crime, there are generally three elements:
• the defendant is the perpetrator,
• the defendant intended to cause death, and
• the defendant's acts caused the victim's death.
These three findings are the "ultimate issues" in a prosecution for murder.
Forensic evidence can also be classified depending on whether it is based on a class characteristic or an individual characteristic. For example, if a size 10 shoeprint is found at a crime scene and a suspect wears a size 10 shoe that looks similar, the shoeprint is only a class characteristic. In order to become an individual characteristic, the shoeprint at the crime scene must have some unique feature (such as a wear pattern, a tack stuck in the sole, etc.) that makes the shoeprint unique. Otherwise, the suspect's shoe is simply in a class of prints that are included in the crime scene print. If, on the other hand, the suspect wears a size 7 shoe, the suspect can be excluded as the source of the print. Class characteristics are useful primarily to exclude.
An individual characteristic is a DNA match at all 13 loci tested in a typical DNA test. As we will see in the DNA chapter, such a "match" means that it is virtually certain the suspect is the source of the DNA (but not necessarily proof of how the DNA was deposited at the site or when). Chapter 4, "The Scientific Method and 'Junk Science,'" explains more about forms of forensic evidence and what they can prove.
Most forensic evidence is circumstantial evidence. That means it may prove a fact from which the jury will need to infer or conclude another fact in order to reach a decision about guilt or innocence. The jury is not required to find that each circumstantial fact is true beyond a reasonable doubt, as long as the cumulative evidence proves guilt beyond a reasonable doubt. The level of certainty for beyond a reasonable doubt is not 100%. Proof beyond a reasonable doubt is proof that precludes every reasonable hypothesis except guilt and is inconsistent with any other rational conclusion.
Hearsay evidence is evidence of statements made by someone who is not in court to testify or be cross-examined about the statement. It is generally not admissible. Reports of forensic tests that contain conclusions are considered hearsay. They may not be admitted in court without the person who made the conclusions being available to be cross-examined. The Confrontation Clause of the U.S. Constitution also requires that a defendant be able to cross-examine all witnesses against him, including any forensic analyst whose report is "testimonial" in nature. We will consider the Confrontation Clause in Chapter 2, "The Court Process."
Forensic evidence requires an expert to explain the significance of the evidence to the jury. The jury is free to accept or reject the testimony of an expert witness, just as for any other witness. There are rules of court that govern experts. At the federal level, the rules are Federal Rules of Evidence 702, 703, and 705, which govern the admission of forensic evidence in all federal trial courts. Most states have similar rules. You will learn about other rules governing trials in the chapter called "The Court Process."
Based on this chapter, students will be able to:
1. Define forensic evidence.
2. Understand the standard of evidence for a verdict.
3. Understand Federal Rules of Evidence 702, 703, and 705.
4. Appreciate the jury's role as finder of fact.
5. Understand court instructions that explain a jury is free to reject an expert opinion.
6. Distinguish between direct and circumstantial evidence.
7. Describe the ultimate issues in a criminal trial and be able to identify their relationship to the legal elements of a crime.
8. Define the hearsay rule and the exception in the Crafts case.
9. Identify the legal standard of proof for ultimate issues determined by one or more inferences from circumstantial evidence.
The term "forensic" does not mean "scientific." It means "of or used in legal proceedings or formal debate."1 Forensic evidence consists of any physical thing that can be used in a court of law as evidence of a fact in issue. Although we think of forensic evidence as relating only to criminal trials, it also applies to civil matters, such as whether a particular drug causes injury. Forensic psychology is used to determine which parent would be best suited to have custody. Forensic accounting is used to determine the value of business assets.
As we will discuss, forensic evidence is evidence resulting from a scientific test or analysis to be used in a criminal trial. This includes: physical items discovered in the course of investigating a crime, such as a gun, knife, document, photograph, piece of clothing, etc. The evidence to be admitted must be "authenticated" by a witness who can identify it and explain its "chain of custody," which means how it got from the crime scene to the courthouse. See Chapter 3, "Crime Scene Investigation." It also includes the results of tests conducted by investigators, such as tests of DNA, fingerprints, fiber, hair, or dental records. Finally, it may involve the results of experiments designed to reconstruct a crime or crime scene, involving the forensic science of ballistics or blood spatter. See Chapter 3.
In 2009, The National Research Council published a report (the NRC Report) called Strengthening Forensic Science in the United States.2 It examined the scientific reliability of many areas of forensics, as follows:
• fingerprints
• firearms examination
• tool marks
• bite marks
• impressions (tires, footwear)
• bloodstain pattern analysis
• handwriting
• hair
• DNA
• coatings (e.g., paint)
• chemicals (including drugs)
• materials (including fibers)
• fluids
• serology
• fire and explosive analysis
• digital evidence
The NRC Report recommended further testing to show scientific reliability in each of these areas of forensic evidence except DNA. Even for DNA, it recommended standards for training, laboratories, and reporting. We will review many of these in the chapters to come.
Proof of Ultimate Issues
Forensic evidence, by itself, does not prove guilt. It is admitted to prove or disprove a fact in a criminal trial that may lead to a finding of guilt. The two most frequent facts are:
1. The identity of the perpetrator.
2. What happened at the crime scene.
"Ultimate issues" are issues which the jury must decide in order to determine its verdict. They are generally determined by the definition of the crime. For the crime of murder, the ultimate issues are the legal elements of the crime. These include generally (1) whether the defendant is the person who committed the crime, (2) whether the defendant acted with the intent required for the specific crime, and (3) whether, in accordance with that intent, the defendant carried out the act or acts necessary to commit the crime.
The Federal Rules of Evidence prohibit an expert from giving an opinion about an ultimate issue, although the opinion may "embrace" an ultimate issue:
Rule 704. Opinion on an Ultimate Issue
(a) In General — Not Automatically Objectionable. An opinion is not objectionable just because it embraces an ultimate issue.
(b) Exception. In a criminal case, an expert witness must not state an opinion about whether the defendant did or did not have a mental state or condition that constitutes an element of the crime charged or of a defense. Those matters are for the trier of fact alone.
Standard of Proof
The jury is not required to find that each fact is true beyond a reasonable doubt, as long as the cumulative evidence proves guilt beyond a reasonable doubt. The level of certainty for beyond a reasonable doubt is not 100%. Proof beyond a reasonable doubt is proof that precludes every reasonable hypothesis except guilt and is inconsistent with any other rational conclusion.
Typically, forensic evidence, by itself, will not prove guilt or innocence. The jury reaches a verdict: guilty or not guilty. It makes that one decision and is not required to explain what other facts it decided were true or not. For example, a jury could reject the defendant's alibi evidence and still conclude that the prosecution had not proved its case beyond a reasonable doubt. We rarely know what facts a criminal jury has determined to be true in giving its verdict.
Identification
Identifying a suspect can result from eyewitness identification. It can also result indirectly from DNA, fingerprinting, and handwriting analysis. Examples of the type of forensic evidence used to identify a perpetrator are as follows:
1. DNA in a sperm kit that matches the defendant's DNA....
2. Defendant's fingerprint on a weapon he owns and that was used to kill the victim.
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