## Facts

- Police pursued a van connected to an armed robbery of a pizza shop in Hyattsville, Maryland; three occupants fled on foot, including Anthony John Casella.
- Police believed one fleeing suspect still had the handgun, though it had been discarded.
- Casella and Tammy Obloy hid in a very narrow passageway between a wall and a fence with limited exits.
- Corporal Joseph Wing arrived with a police dog, Iron, tracked the suspects, and released the dog into the passageway; Wing testified he warned the suspects before release, while Obloy testified she heard no warning.
- Iron bit Obloy, and Casella kicked the dog; officers then converged on the passageway.
- Plaintiff’s evidence indicated Iron bit Casella multiple times and officers struck Casella with a slapjack and flashlight, causing severe head injury and other trauma.
- Casella later pleaded guilty to armed robbery, filed a 42 U.S.C. § 1983 action alleging excessive force, and died in prison; his mother, Ada Sandra Kopf, continued the suit as estate representative.
- After an earlier appeal remanding for trial, the district court excluded two police-practices experts (on canine deployment and slapjack use), admitted evidence about Casella’s conviction and drug/criminal history, and a jury returned a defense verdict for the officers and the County.

## Issues

1. Whether the district court abused its discretion under Federal Rule of Evidence 702 by excluding expert testimony on proper police use of dogs and slapjacks in an excessive-force trial.
2. Whether evidence of Casella’s later armed-robbery conviction and other criminal/drug activity was relevant to objective reasonableness or was unfairly prejudicial under Rules 401–403.
3. Whether evidence of a prior arrest incident involving an officer could be admissible as prior-acts evidence under the Federal Rules of Evidence.
4. Whether municipal liability required proof that a county policy or custom caused the alleged constitutional violation rather than respondeat superior liability.

## Decision

- The Fourth Circuit reversed the judgment and remanded for a new trial.
- The court held the district court abused its discretion by excluding qualified expert testimony on police canine deployment and slapjack use because such topics are typically outside ordinary juror knowledge and would assist the jury under Rule 702.
- The court held Casella’s ultimate conviction for armed robbery was irrelevant to whether the force used during the arrest was excessive and that related character evidence risked unfair prejudice.
- The court indicated that evidence of a prior arrest incident involving an officer could be admissible on retrial if offered for a proper non-character purpose and subject to evidentiary safeguards.
- The court reaffirmed that the County could be liable under § 1983 only if a policy or custom caused the constitutional violation.

## Legal Principles

- Expert testimony is admissible under Fed. R. Evid. 702 when specialized knowledge will assist the jury; police practices regarding canine deployment and specialized weapons may warrant expert explanation in excessive-force cases.
- Fourth Amendment excessive-force claims turn on objective reasonableness at the time of the arrest; an arrestee’s later conviction is generally irrelevant to that inquiry.
- Under Rules 401–403, marginal relevance may be outweighed by unfair prejudice where criminal-history or drug-use evidence risks shifting the jury’s focus from officer conduct to the plaintiff’s character.
- Prior-acts evidence may be admissible for a permissible purpose under the Federal Rules of Evidence (not to prove character), depending on the theory of relevance and limiting measures.
- Municipal liability under § 1983 requires proof that an official policy or custom caused the constitutional injury; municipalities are not liable on a respondeat superior theory.

## Conclusion

The Fourth Circuit ordered a new trial because the exclusion of police-practices experts and the admission of prejudicial character evidence prevented the jury from fairly evaluating the objective reasonableness of the force used during Casella’s arrest and distorted the evidentiary framework for both individual and municipal liability.


Kopf v. Skyrm, 993 F.2d 374 (4th Cir. 1993)