Reversal was required where a juror engaged in prejudicial misconduct by concealing a felony conviction that would have disqualified him from jury service under California law. The state Court of Appeal’s finding that the juror’s misstatements, both on a jury questionnaire and during voir dire, were not deliberate was an unreasonable determination of the facts. The juror expressed no confusion about the question, which inquired about his involvement in any prior assault. It was unreasonable to conclude that he had “forgotten” it, since he served time in prison. He also made statements during jury deliberations about knowing that Green was guilty, “the minute he saw him.” The juror’s pattern of lies, inappropriate behavior, and attempts to cover up his lies and behavior introduced uncertainty into the fact-finding process, and bias could be presumed.