On Wednesday, the Minnesota attorney general charged four former Minneapolis police officers for their roles in the murder of George Floyd, the black man whose death has sparked days of worldwide protests. Derek Chauvin, the officer filmed pressing his knee into Floyd's neck while he begged for his life, was charged with second-degree murder.

That new charge, filed in an amended complaint, marked a shift in the case. Two days earlier, the governor had asked Attorney General Keith Ellison to take over the criminal investigation started by Hennepin County Attorney Mike Freeman. It was a step toward "justice for George Floyd," Gov. Tim Walz said. Freeman's office will work together with Ellison's office on the case.

A week before, Freeman's office had charged Chauvin with the lesser crimes of third-degree murder and second-degree manslaughter. The three other officers weren't charged at that time.

The local prosecutor's initial court filing puzzled criminal justice experts, not only because of the charges, but also the way the allegations were crafted. For some, it called into question the prosecution's commitment to its own case, demonstrating wider challenges to securing convictions against police who abuse their authority.

The first complaint detailed how Floyd "struggled with the officers by intentionally falling down." It described him saying "I can't breathe," but failed to mention some of his most damning dying words, captured by cellphone videos that spread across the internet: "Please — the knee in my neck," and "I'm about to die."

The court filing noted Chauvin pressed his knee to Floyd's neck for nearly nine minutes, and that during the last three minutes, Floyd was unresponsive. Police are trained to know that the way Chauvin held Floyd down is "inherently dangerous," the complaint said.

But it also detailed Floyd's underlying health problems, "coronary artery disease and hypertensive heart disease," and cited the medical examiner's preliminary findings that those health conditions, the officers' restraint tactics, and intoxicants in Floyd's system "likely contributed to his death."

It was an unusual admission for a charging document, according to Hinshaw & Culbertson LLP partner David Weinstein, who served for two decades as a prosecutor in Florida. Criminal complaints, he said, tend to take on a more neutral tone when charging law enforcement officers. This complaint was so neutral, he said, at times it seemed to be arguing against itself.

"Coronary artery disease is high cholesterol. That means you've got some fat deposits. Hypertensive heart disease means you have high blood pressure. I think there are a large number of people that have both of those. That's not going to kill you," he said. "For them to focus on that, I think that they're going a little past being neutral."

The fact the county attorney's office pointed to weaknesses in its own case reveals a more chronic issue in law enforcement, according to Michael Haddad, a member of the National Lawyers Guild's National Police Accountability Project: prosecutors' reluctance to go after police officers.

"To me, it looks like this prosecutor is biased in favor of the police, and doesn't want to do his job, which is probably why the state attorney general's office took over," he said of the original complaint.

And the weakness of the complaint suggests to A.L. Brown, a St. Paul-based criminal defense attorney with Capitol City Law Group LLC, that Freeman's office had no intent of going to trial.

"This is not enough to survive probable cause," he said of the initial complaint. "We've got some really, really talented defense attorneys here in the Twin Cities who are on contract with the police federation. These guys are going to eat this complaint up. Mike Freeman is going to force a judge, if the judge follows the law, to just kick this third-degree complaint."

The amended complaint with the upgraded charge against Chauvin spent less time on the weaknesses of the case and built up evidence of Floyd's distress.

It, too, mentioned his health conditions, but added new details from the coroner's report finding the cause of death was "cardiopulmonary arrest while being restrained by law enforcement officers," and noted that Floyd "repeatedly stated he could not breathe and his physical condition continued to deteriorate such that force was no longer necessary to control him."

It also notes that "Floyd told the officers that he was not resisting but he did not want to get in the back seat and was claustrophobic," and included Floyd saying he was dying.

Prosecutors can be reluctant to go after the law enforcement officers with whom they frequently work closely. That makes police accountability challenging. It's one of the reasons why when a police officer kills someone on the job, about 99% of the time, no charges are filed.

The Floyd case is unusual because charges were filed, Haddad said, but he added that the initial complaint suggests a larger truth about the likelihood of bringing successful charges in such cases.

"It's extremely rare for any officers to ever get charged," Haddad said. "The only time it seems to happen is when there is video and they're caught red-handed."

It's raised a question for many advocates: Would any of the officers have faced consequences if Floyd's death hadn't sparked national outcry?

The statistical chances of Chauvin facing consequences would be slim — less than 2%, according to Mapping Police Violence, a group that's compiled nationwide data on police killings since 2013.

Police killed 7,663 people between 2013 and 2019. Only 101 of those deaths led to criminal charges against the officers involved, and 26 led to convictions.

And though African Americans make up about 13% of the U.S. population, they accounted for 24% of deaths at the hands of police. A black suspect is three times more likely than a white suspect to be killed by a police officer, according to Mapping Police Violence.

It took four days for prosecutors to file the first complaint against Chauvin. Other infamous cases of black suspects dying at the hands of police took much longer to yield charges, if they did at all.

It took two months to bring before a grand jury the case against the New York police officer who killed Eric Garner by strangling him with a chokehold in 2014. It took four months to bring charges against the officer who shot Philando Castile in his car in a Twin Cities suburb in 2016. Neither of those led to a conviction. The police who fatally shot Breonna Taylor when they entered her apartment in Louisville, Kentucky, with a no-knock warrant back in March still haven't been charged.

Paul Callan, who served as deputy chief of homicide at the Brooklyn District Attorney's Office before joining Edelman & Edelman PC, said one reason police are rarely prosecuted has to do with the strength of the case.

He pointed to Michael Brown, the black teenager who was shot six times by a police officer in Ferguson, Missouri, sparking national outrage. It was an "iconic case of police brutality" to protesters, Callan said, "but the grand jury believed deadly force was justified."

"Most prosecutors only want to bring cases that they know they can win," he said. "You only have to have probable cause to bring charges, but most prosecutors want enough evidence to say they have a reasonable chance of getting a conviction from a jury."

But another reason so few police killings result in prosecution could be that police and prosecutors are usually allies, and attorneys feel reluctant to go after the officers they rely on to do their jobs. That may be part of the reason the attorney general's office joined the Chauvin case — the office rarely works closely with local law enforcement.

"Having been a former homicide prosecutor myself, I think that's a fair criticism," Callan said. "There does tend to be a relationship between the prosecutor and police. Prosecutors see so many horrible things, they have an understanding of what a difficult job being a street cop is, and I think they tend to develop a sympathy for police that robs them of some of their objectivity."

Investigators, too, may be compromised. The agent who worked on the Floyd case, Minnesota Bureau of Criminal Apprehension Special Agent Michelle Frascone, has faced prior allegations that called into question her objectivity.

Frascone, who worked for many years as a police officer in the Minneapolis suburb of Woodbury, was sued in a civil case over the death of Jamie Joseph Lewis. In 2016, Lewis' girlfriend called the police to report that he was depressed, suicidal and had a gun. One of the officers who responded to the scene shot him.

Frascone investigated his death, and according to the suit brought by Lewis' family, she coached one of the officers who'd responded to the 911 call, suggesting "Lewis' intent may have been not merely to end his own life, but to murder other people as well," according to the complaint, which said the officer revised his statement at Frascone's prompting.

The conspiracy claim against Frascone was dismissed, with a federal judge finding Lewis' family didn't have standing to sue her. The Lewis family's attorney didn't respond to requests for comment, nor did the Minnesota BCA.

Haddad said such leading questions are the norm during these investigations.

"We see this most of the time. When a police officer has shot or killed someone and they're being interviewed afterward, it's so common for the police interviewer to be throwing out softball questions, to be suggesting the right answer for the officer, like, 'Were you afraid for your life?'" he said.

"Unfortunately, I almost never see an aggressive interrogation of an officer who's just killed somebody," Haddad added. "Not the way they would talk to somebody else who's not a police officer."

That kid-glove treatment can continue when the case gets to the prosecutor, who might choose not to pursue the case or to do so halfheartedly.

Brown, the local criminal defense attorney, called the initial Chauvin complaint "shameful." He said Freeman "doesn't like being told what to do," and that the complaint's odd tone reflected that he felt forced into filing it.

"He is no doubt smarter than the document he let leave his office," Brown said. "I've never read a probable cause statement with more exculpatory evidence in it in my life. You won't find another one that reads like that."

The county attorney's office didn't answer questions about the charges it chose or the language of the complaint, but sent Law360 a statement.

"Our office reviewed evidence ranging from the citizen's video to the officer's body worn camera," it said. "We also spoke to witnesses, had a preliminary report from the medical examiner and had discussions with an expert. All of the evidence came together, and we felt in our professional judgment, that it was the correct and right time to charge."

To some former prosecutors, the initial complaint signaled not a shirking of duty, but an effort to appease the public by filing quickly. Callan said the "odd" choice of outlining weaknesses in the case may have reflected the fact that Freeman filed charges before all the facts, including the final autopsy report, were in.

"I think they were hedging and seeding a message to the public: 'The reason I'm not charging him with intentional murder is there's a problem here with causation and preexisting conditions,'" he said.

Third-degree murder, the original charge brought against Chauvin, is rarely used in Minnesota, according to the state's former U.S. attorney, Thomas Heffelfinger, now an attorney at Best & Flanagan LLP.

The charge would require proof that Chauvin had a "depraved mind" and was reckless. The newer charge, murder in the second degree, only requires prosecutors show Chauvin committed the felony of assault, which led to Floyd's death.

"Unintentional second-degree murder while committing a felony specifically does not require proof of intent," Heffelfinger said. "That's important, because it's inherently difficult to prove intentional crimes."

That means the second-degree murder charge added in the amended complaint is both easier to prove and more serious. Third-degree murder carries a maximum 25-year sentence, while second-degree murder carries a 40-year sentence.

When he announced the additional second-degree murder charge, as well as aiding and abetting murder charges for the other three officers on Wednesday, Minnesota's attorney general acknowledged the public's mistrust of the justice system, which has historically failed to hold "people who are public guardians accountable for their behavior."

"Our country has underprosecuted these matters," Ellison said. "We can't control the past; all we can do is take the case we have in front of us right now and do our good faith best to bring justice to the situation, and we will."

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--Editing by Katherine Rautenberg.

Clarification: This article has been updated to clarify how Mapping Police Violence presented its data.