## Facts

- Robert Gaskell’s infant daughter, Kristen, had recurring episodes of vomiting and medical treatment in the months before her death.
- On February 10, 1990, Kristen vomited; after her mother left, she remained in Gaskell’s care.
- Neighbors trained as EMTs responded when Gaskell sought help, found Kristen pale and not breathing with vomit present, and attempted resuscitation until paramedics arrived; Kristen was pronounced dead that evening.
- The medical evidence was disputed:
  - The local medical examiner reported internal trauma and interpreted neck findings as consistent with strangulation or head impact.
  - A government expert attributed the death to shaken baby syndrome (SBS) and characterized the neck finding as a rash.
- Over objection, the trial court allowed the government expert to demonstrate SBS by forcefully shaking a CPR infant mannequin, stating the mannequin’s neck was stiffer than a real infant’s and thus required greater force to produce comparable head motion.
- The defense theory was that any shaking was a panicked attempt to revive a non-breathing infant, not an intent to harm; defense experts sought to support that SBS-type findings could be consistent with misguided resuscitation efforts.
- A federal jury convicted Gaskell of involuntary manslaughter under 18 U.S.C. § 1112.

## Issues

1. Whether admitting a shaken-baby courtroom demonstration using a CPR mannequin was an abuse of discretion because the conditions were not substantially similar and the probative value was substantially outweighed by unfair prejudice under Federal Rule of Evidence 403.
2. Whether excluding or limiting defense expert testimony supporting an alternative, non-culpable explanation for the medical findings improperly impaired the defense.
3. Whether the jury instructions correctly conveyed the mens rea and foreseeability requirements for involuntary manslaughter under 18 U.S.C. § 1112.

## Decision

- The Eleventh Circuit reversed the conviction.
- The court held the SBS mannequin demonstration should not have been admitted because key physical differences from an actual infant (including a stiffer neck requiring greater force) reduced probative value and increased the risk of misleading and inflaming the jury.
- The court concluded that the handling of expert evidence and the overall presentation at trial contributed to an unfair adjudication of the disputed medical-causation and culpability questions.
- The errors were not harmless in a case turning on competing expert interpretations and the defendant’s claimed emergency-rescue explanation.

## Legal Principles

- Courtroom demonstrations and experiments are admissible only if the proponent shows substantial similarity between the demonstration conditions and the event at issue; dissimilarities may render the evidence misleading.
- Under Federal Rule of Evidence 403, demonstrative evidence with limited probative value may be excluded if it creates a substantial danger of unfair prejudice, including emotional impact that invites jurors to equate the demonstration’s force with the defendant’s conduct.
- Involuntary manslaughter under 18 U.S.C. § 1112 requires proof of culpability beyond ordinary negligence, commonly framed as gross negligence or wanton/reckless disregard for human life, including that the defendant should have foreseen the lethal risk created by the conduct.
- In medically complex prosecutions, restricting defense expert testimony bearing on causation and culpability can distort the adversarial presentation where the government is permitted highly persuasive scientific evidence.

## Conclusion

The Eleventh Circuit reversed Gaskell’s involuntary manslaughter conviction because the prosecution’s shaken-baby mannequin demonstration lacked sufficient similarity to real-world conditions and posed a substantial risk of unfair prejudice, and the trial’s evidentiary and instructional framework did not reliably test whether the government proved the required level of culpable, foreseeable risk under § 1112.


United States v. Gaskell, 985 F.2d 1056 (11th Cir. 1993)