The problem was that the trial judge made all sorts of bad rulings and admitted (or let the jury hear about) a host of irrelevant, prejudicial, and inflammatory evidence on things like gangs, drugs, and weapons that had no bearing whatsoever on the reasonableness of the shooting. Swayed by this irrelevant evidence, the jury deliberated for less than two hours before finding the officer not liable for killing Manual Diaz.
The family of Manual Diaz appealed and recently won their appeal at the Ninth Circuit level. The Ninth Circuit held that the trial court in Estate of Diaz v. City of Anaheim abused its discretion in making certain rulings and in allowing the jury to hear about prejudicial and irrelevant evidence. Among the troubling evidence was testimony by a "gang expert," photographs of Manual Diaz "throwing" gang signs, photographs of Manual Diaz with weapons, and evidence of drug use.
The Ninth Circuit held that such alleged evidence was not relevant to the central issue of liability -- whether or not the shooting was reasonable under the circumstances in light of excessive force law. To the extent that some such evidence may have had a bearing on another aspect of the case (such as damages), the judge did not take appropriate measures to limit the evidence for those purposes -- and thus to keep it from irreparably tainting the jury's verdict on liability.
For example, the Ninth Circuit explained that the judge should have bifurcated the trial to allow certain evidence in the liability phase and other evidence in the damages phase. "Considering that the parties and district court had repeated trouble tracking precisely why this prejudicial evidence was admissible for any purpose, no jury could properly compartmentalize it," the court held. "Even assuming that a portion of this evidence had some relevance to damages, it never should have been combined with the liability phase."
In its order sending Estate of Diaz v. City of Anaheim back to the district court for a new trial, the Ninth Circuit gave the district court "guidance" for what to do the second time around. The guidance included closely reviewing evidence under Federal Rules of Evidence 401 and 403 for relevance and prejudice, consider dealing with the "gang" issue through stipulation, reconsider the efficacy of "limiting instructions," and take better care in handling "stricken" evidence.
Federal Rule of Evidence 401 provides:
Evidence is relevant if: (a) it has any tendency to make a fact more or less probable than it would be without the evidence; and (b) the fact is of consequence in determining the action.
Federal Rule of Evidence 403 provides:
The court may exclude relevant evidence if its probative value is substantially outweighed by a danger of one or more of the following: unfair prejudice, confusing the issues, misleading the jury, undue delay, wasting time, or needlessly presenting cumulative evidence.