In the criminal justice system, the outcome of many criminal law cases will depend upon the strength and admissibility of evidence. Types of evidence in criminal cases that are introduced at a jury trial include:
- Physical evidence (objects, clothing, etc.)
- Scientific and forensic evidence (DNA, ballistics, etc.)
- Witness testimony (crime victims, law enforcement officers, etc.)
Evidence can be complex, but this article will help make sense of the different rules and concepts surrounding evidence in criminal prosecution. Below, you will find information on admissibility, witness testimony, using scientific evidence in district court, and more.
For evidence to be admissible in criminal proceedings, it must be relevant, material, and competent. This standard applies to court proceedings in civil cases as well. To be relevant, evidence must reasonably help prove or disprove some fact. The degree to which this evidence increases or decreases the likelihood of the fact influences the weight given by the judge, grand jury, or trial jury.
Evidence is material if offered to prove a fact in dispute. A court rules evidence is competent if it falls within specific reliability standards. Learn more about the admissibility of evidence and how these rules get interpreted and applied.
Otherwise-admissible evidence is suppressible when it has been illegally obtained. Such as in a violation of a criminal defendant's constitutional rights. For example, evidence obtained without a search warrant or probable cause. Despite a defendant's guilt, a defense attorney would likely win a motion to suppress the wrongly obtained evidence.
Evidence produced as a result of the following may get suppressed:
- An unlawful search and seizure
- The failure to read Miranda rights
- A broken chain of custody
Any evidence produced due to these flawed circumstances is the "fruit of the poisonous tree." But, evidence may still get admitted under the following conditions:
- Where it would have been inevitably discovered
- The officer was acting in good faith
- An independent source would have produced the same evidence
Hearsay describes when a witness repeats a third-party, out-of-court statement in court to prove the truth of the statement itself. For example, "My neighbor told me he saw her attack the victim." Generally, hearsay is not admissible due to its unreliability. But, the Federal Rules of Evidence provide exceptions to the hearsay rule.
The Federal Rules of Evidence (FRE) list 24 exceptions. This includes a catch-all rule. Hearsay evidence that doesn't otherwise fit into the exceptions is still admissible if:
- It has sound guarantees of trustworthiness
- It helps prove a material fact
- It is more probative than other similar reasonably obtainable evidence
- It would forward the cause of justice
- All parties have been notified that it will be offered as evidence
Learn more about hearsay evidence and the unique circumstances in which it's considered in court.
Character evidence usually is not permitted in criminal court to show a person is likely guilty. It also can't be used to show that the person acted in conformity with that character trait on a particular occasion. For example, a person's reputation for exaggeration or lying is not admissible as evidence that the person committed fraud.
There are some limited circumstances when character evidence is allowable. For example, FRE 608 allows attacks on the witness's credibility. When this happens, evidence of their character for truthfulness or untruthfulness is then introduced on cross-examination.
At the sentencing stage, character evidence is often introduced. Here, it is not to prove guilt but rather to argue for leniency or strictness in punishment. Criminal defense attorneys will submit evidence of a defendant's good character. Witnesses attest to their favorable qualities, such as kindness, generosity, and community service.
The district attorney (prosecutors) will introduce the defendant's negative criminal record to argue for a stricter sentence. Suppose a defendant faces a criminal charge for assault and gets convicted. Any prior assaultive conduct is highly relevant at sentencing. For example, prior criminal convictions such as misdemeanor or felony cases of domestic violence would likely result in a longer sentence or harsher penalty.
Civil suits have similar rules, but exceptions exist, especially in defamation suits and others where character is potentially central to the claim. Additionally, under FRE 406, habit rather than character is admissible as evidence when it is:
- Consistently repeated
An individual's habit is more specific than character because it's almost semi-automatic. An organization's routine practice, for example, a document retention policy, is admissible to show the company acted in accordance with the habit or routine practice.
Learn more about character evidence, the concept of admissibility, and other issues that affect a criminal case in the pretrial, plea bargaining, and trial phases.
Scientific and Forensic Evidence
Scientific and forensic evidence is objective and unbiased information that helps prove or disprove a fact using peer-reviewed professional and academic standards. There are many kinds of scientific evidence admitted to criminal courts, including:
- Fiber analysis
- DNA and other blood evidence
Any scientific evidence produced at trial must be well established within the scientific community and generally accepted as true before assertion at trial. Fingerprint and DNA matching are reasonably well-understood, but there are times when less established kinds of scientific evidence get introduced.
FRE 702 governs testimony by expert witnesses. A witness qualifies as an expert by knowledge, skill, experience, training, or education. The witness can provide testimony in the form of opinion where:
- The expert's scientific, technical, or other specialized knowledge will help the trier of fact to understand the evidence or to determine a fact in issue
- The testimony is based on sufficient facts or data
- The testimony is the product of reliable principles and methods
- The expert has reliably applied the principles and methods to the facts of the case.
Often, the prosecution and defense will attempt to introduce expert testimony to bolster their interpretation of scientific evidence to either get an acquittal or a conviction. When necessary, an evidentiary hearing on the validity of a scientific theory takes place before the trial on the merits of the principal case.
Two primary standards govern the admissibility of an expert witness: the Frye and Daubert standards. In 1923, in Frye v. United States, the U.S. Court of Appeals for the District of Columbia Circuit established a rule that the results of a scientific test are admissible as evidence only when the test or procedure has gained general acceptance in the scientific community as reliable (peer-reviewed).
However, in 1993, the Supreme Court held in Daubert v. Merrell Dow Pharmaceuticals that the FRE superseded the Frye test. Scientific evidence (such as expert testimony) must meet only the factors listed above for admissibility. Learn more about different kinds of forensic evidence and their current reception by courts.
Learn More About Criminal Evidence From a Criminal Defense Attorney
Law enforcement agencies use various investigative methods that must stand scrutiny at both the criminal trial and appellate level. Each side will attempt to undermine the other, and the defense will highlight weak evidence to raise reasonable doubt.
In the face of unfavorable evidence, an experienced defense attorney can:
- Negotiate a guilty plea and favorable plea agreement
- Highlight constitutional and criminal procedure violations (e.g., self-incrimination)
- Emphasize weaknesses in the prosecution case during the opening statement
If you have questions about your criminal case, talk to an attorney in your area. An attorney can advocate for you from the first court date (arraignment) and request a speedy trial date.