In Minneapolis, the tension is palpable as the city awaits the outcome of the trial of Derek Chauvin, the police officer accused of murdering George Floyd last summer. The court proceedings have been both emotional — the video of Mr. Floyd’s death has been played over and over — and technical. At the heart of the case: How did Mr. Floyd die? Today, we look at the case that has been brought against Mr. Chauvin so far.