MINNEAPOLIS — A Minneapolis police officer was swiftly fired and charged with murder after bystander video showed him pressing his knee into George Floyd's neck, ignoring the Black man's cries that he couldn't breath. But even with that powerful footage, legal experts say the case isn't a slam dunk.

Jury selection begins Monday in Derek Chauvin's trial, which is expected to come down to two key questions: Did Chauvin's actions cause Floyd's death, and were his actions reasonable?“It's hard not to watch the video and conclude that the prosecutors will not have any trouble with this case,” said Susan Gaertner, the former head prosecutor in neighboring Ramsey County. “But it's not that simple.”Floyd was declared dead May 25 after Chauvin, who is white, pressed his knee against Floyd's neck for about nine minutes, holding his position even after Floyd went limp as he was handcuffed and lying on his stomach. Floyd's death sparked sometimes violent protests in Minneapolis and beyond, and led to a nationwide reckoning on race.Chauvin is charged with second-degree unintentional murder and second-degree manslaughter, and a panel of appeals court judges ruled Friday that the judge must consider reinstating a third-degree murder charge that he dismissed last fall. Three other officers, all of whom also were fired, face trial in August on charges of aiding and abetting the second-degree murder and manslaughter counts.The second-degree murder charge requires prosecutors to prove Chauvin caused Floyd's death while committing or trying to commit a felony — in this case, third-degree assault. The manslaughter charge has a lower bar, requiring proof that Chauvin caused Floyd's death through negligence that created an unreasonable risk, and consciously took the chance of causing severe injury or death.Exactly how Floyd died is shaping up as a major flashpoint of the trial.Chauvin's attorney, Eric Nelson, argues in court documents that Floyd likely died from fentanyl he consumed, or a combination of fentanyl, methamphetamine and underlying health conditions — not as a result of Chauvin's knee on his neck.But Hennepin County Judge Peter Cahill wrote last fall that for the second-degree murder charge, prosecutors don't have to prove that Chauvin was the sole cause of Floyd's death — only that his conduct was a “substantial causal factor.”

Derek Chauvin