Did former Minneapolis police officer Derek Chauvin act reasonably and within his authority when he applied force during the arrest of George Floyd? And did those actions, including his knee pressed on the neck and back of the 46-year-old Black man, result in his death?
These are the two main questions jurors will have to consider as they retire to deliberate the legal fate of Chauvin Monday after three weeks of testimony.
Chauvin is on trial in Hennepin County District Court in Minneapolis on charges of second-degree unintentional murder, third-degree murder and second-degree manslaughter in the death of Floyd.
"If the prosecution can't prove that Derek Chauvin was the cause of George Floyd's death or substantially caused his death, then Derek Chauvin can't be found guilty in terms of his death," said David Schultz, a University of Minnesota law professor.
"I think the two major points that the jury's going to have to think about: Was Chauvin acting within his legal authority? Did he cause the death or substantially cause the death of George Floyd?"
Floyd died on May 25, 2020, after Chauvin, who is white, pressed his knees on his neck and back for about nine minutes as two other officers held him face down on the pavement while he was handcuffed. He had been detained outside a convenience store on suspicion of paying with a counterfeit bill.
A battle of the experts
The two murder charges Chauvin faces carry maximum prison sentences of 40 years and 25 years, respectively, but sentencing guidelines for first-time offenders mean Chauvin would likely serve 12 and a half years if convicted. The guidelines give the judge discretion to hand down a sentence between 10 and 15 years.
The lesser charge of manslaughter has a maximum sentence of 10 years and a presumptive sentence for first-time offenders of four years.
If Chauvin is convicted, the prosecution is expected to argue for a longer imprisonment than the presumptive sentence, possibly on the grounds that there were aggravating factors, such as that the crime occurred in the presence of a child (one of the bystanders was nine years old).
As the jury retired Monday, the city of Minneapolis was on high alert, preparing for potential violence in the event of an acquittal.
The outcome of the high-profile trial is being closely watched across the U.S. and around the world after video of Floyd's arrest captured by a bystander prompted widespread outrage, setting off protests over racism and police brutality that began late last May.
The jury will have to sift through 14 days of evidence that included scores of exhibits, video and testimony from 45 witnesses, most of whom were called by the prosecution.
'In some sense, this case is a battle of the experts," said Ronald Sullivan, a law professor at Harvard Law School and director of the university's Criminal Justice Institute.
"If the jury believes that the substantial causal factor of the death was a police action, then the question is whether the police conduct was reasonable. Whether the use of force was reasonable."
Sullivan represented the family of Michael Brown, a Black teen killed by a police officer, in reaching a settlement with the City of Ferguson, Mo., on a wrongful death claim
WATCH | Lawyer for Floyd and Wright families reacts to Chauvin trial:
On the question of whether the officer's actions were reasonable, the prosecution elicited testimony from use-of-force experts, including from within the city's own police force. Several of them agreed the actions of Chauvin, who had been trained in use-of-force tactics, were excessive.
The city's police chief, Medaria Arradondo, testified that Chauvin violated police policy and should have stopped kneeling on Floyd once Floyd had stopped resisting and signalled he was in distress.
The defence countered with one witness of its own, Barry Brodd, a former officer in Santa Rosa, Calif., who said Chauvin was justified to take the measures he did and was acting with "objective reasonableness."
Officers have statutory authority to use force when they operate within the line of duty and they are clearly empowered to use force to protect themselves or the public, said Schultz, the University of Minnesota law professor.
The U.S. Supreme Court, through a variety of decisions, has said officers enjoy a "qualified immunity" to use force if they're acting reasonably, as a reasonable officer, he said.
Schultz said the prosecution's use-of-force arguments were critical in the trial to try to establish that Chauvin was not following department procedure or protocol or following state law when he forced Floyd to the ground and kneeled on his neck. Rather, they aimed to demonstrate, he was acting beyond what a reasonable officer would do.
Yet, the defence's best argument might be that the situation on the ground in real time required Chauvin to take the steps he did, said Sullivan, the Harvard law professor.
Some of the prosecution's own witnesses testified upon cross-examination that sometimes, people who have lost consciousness can be violent when they come to, he said.
One officer on the scene testified the crowd was becoming increasingly unruly and distracted the officers from the care of Mr. Floyd, Sullivan said.
Cause of Floyd's death
Finally, the jury will have to determine the cause of Floyd's death.
Ted Sampsell-Jones, a law professor at the Mitchell Hamline School of Law in St. Paul, Minn., says the prosecution had to prove Chauvin's conduct was a "substantial contributing factor" to Floyd's death.
Court heard from several prosecution medical witnesses who testified that Floyd died of positional asphyxia, meaning his oxygen was cut off as he was pinned to the ground face down while Chauvin pressed his knee into his neck and back for more than nine minutes.
Certainly some of the most-powerful pieces of evidence for the prosecution were the videos, from bystanders, police body cameras and surveillance cameras, showing Floyd pressed to the pavement, pleading that he couldn't breathe, before he eventually became unresponsive and police were heard saying they couldn't find a pulse.
Sampsell-Jones said the video will have an impact on the jury.
"At the end of the day, they're going to be mostly influenced by the video in this case," he said. "I mean, that's the thing. That's the one piece of evidence that is so overwhelming."
The defence argued Floyd's death was caused by his pre-existing heart condition combined with the drugs fentanyl and methamphetamine in his system, as well as carbon monoxide from the exhaust of the squad car next to which he was lying and the adrenaline rush from his scuffle with police.
Sampsell-Jones said he believes the defence did a good job describing how this could have led to Floyd's death or at least potentially raising reasonable doubt.
Sullivan said the fact fentanyl was discovered in Floyd's system could pose a problem for the prosecution.
"People know from watching the news and so forth how powerful fentanyl is. [Emergency responders] wear gas masks if they're in the presence of it," he said.
Another potential issue for the prosecution is the testimony from the county medical examiner who conducted Floyd's autopsy. While Dr. Andrew Baker agreed that Floyd's death was caused by the actions of the officers, he didn't list asphyxia as a cause. Instead, he said the police's restrain of Floyd put too much strain on his heart, causing cardiopulmonary arrest.
Baker also said Floyd's heart disease, as well as his history of hypertension and the drugs that were in his system, played a role in his death.
But the prosecution doesn't have to prove that Chauvin was the sole or even primary cause of death, said Sampsell-Jones.
"All they have to show is really that he was a contributing cause," he said. "That's a pretty low bar. So I think the jury, even if it gets a little bit confused about the competing medical evidence, will still probably come down saying that if nothing else, Chauvin was a contributing cause of death.
"And that's enough in Minnesota to count as homicide."