Explainer: How is 'reasonableness' key to Derek Chauvin's defense?

Attorneys and witnesses have used the words "reasonable" or "unreasonable" often at the trial of the former Minneapolis police officer charged with murder and manslaughter in George Floyd's death. It's no coincidence. The concept of reasonableness has been crucial at trials of officers ever since the landmark Graham v. Connor ruling 32 years ago by the US Supreme Court.