Polygraph Use In Criminal Law
What Is a Polygraph?
Measures heart rate, blood pressure, respiration, and skin conductivity during questioning.
Based on the theory that lying causes physiological stress.
Used by law enforcement in investigations, sometimes in pretrial or probation settings.
Not generally accepted as conclusive evidence in court.
Legal Issues Around Polygraphs:
Admissibility: Are polygraph results admissible as evidence?
Reliability: Scientific debates on accuracy and false positives/negatives.
Voluntariness: Must consent be given to take a polygraph?
Use in plea bargains or interrogations.
Key Cases on Polygraph Use in Criminal Law
1. United States v. Scheffer (1998)
Issue: Whether a military court’s per se ban on polygraph evidence violates the defendant’s rights.
Facts: Scheffer wanted to introduce polygraph results to support his defense.
Holding: Supreme Court ruled that military courts can categorically exclude polygraph evidence.
Significance: Affirms that courts can exclude polygraphs without violating due process, emphasizing skepticism about reliability.
2. Frye v. United States (1923)
Issue: Admissibility of scientific evidence, including early polygraph evidence.
Facts: Frye’s conviction challenged due to the polygraph test.
Holding: Established the "Frye Standard" that scientific evidence must be generally accepted by the relevant scientific community.
Significance: Early polygraph evidence was excluded because it did not meet this standard.
3. Daubert v. Merrell Dow Pharmaceuticals (1993)
Issue: Standard for admissibility of expert scientific testimony, impacting polygraph evidence.
Holding: Set guidelines (Daubert Standard) requiring reliability, peer review, error rates.
Significance: Many courts exclude polygraph results because they fail these reliability criteria.
4. People v. Leahy (California, 1994)
Issue: Whether a defendant can introduce polygraph results to prove innocence.
Holding: Court ruled that polygraph evidence is inadmissible except under limited circumstances.
Significance: Highlights cautious approach; polygraphs are not reliable enough for general admission.
5. United States v. Cordoba (2nd Cir., 2010)
Issue: Admissibility of polygraph evidence in federal court.
Holding: The court excluded polygraph results, citing lack of scientific reliability.
Significance: Reaffirms federal courts’ general refusal to admit polygraph evidence.
6. State v. Weinstein (New Jersey, 1984)
Issue: Polygraph used during pretrial phase; whether results can be admitted.
Holding: New Jersey Supreme Court ruled polygraph evidence inadmissible in court but allowed limited use in plea negotiations.
Significance: Shows polygraphs may influence case strategy even if not entered as evidence.
Summary Table
| Case | Court & Year | Issue | Holding | Significance |
|---|---|---|---|---|
| United States v. Scheffer | SCOTUS 1998 | Military court ban on polygraphs | Ban upheld | Courts may exclude polygraph evidence |
| Frye v. United States | D.C. Cir. 1923 | Scientific acceptance test | Polygraphs excluded | Early rejection of polygraph evidence |
| Daubert v. Merrell Dow | SCOTUS 1993 | Scientific evidence standard | Set Daubert standard | Polygraphs often fail reliability test |
| People v. Leahy | California 1994 | Polygraph to prove innocence | Generally inadmissible | Limits on polygraph evidence |
| US v. Cordoba | 2nd Cir. 2010 | Polygraph admissibility | Polygraph excluded | Federal courts skeptical |
| State v. Weinstein | New Jersey 1984 | Pretrial polygraph use | Not admissible but allowed in plea | Polygraphs may influence plea talks |
Important Points:
Polygraphs are generally inadmissible in court due to reliability concerns.
Some courts allow limited use in plea bargaining or investigations.
The scientific community is divided, and polygraphs can produce false positives/negatives.
Defendants cannot be forced to take polygraph tests without consent.
Some states have special rules or allow polygraph evidence if both parties agree.
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