The 2019 conviction of former Minneapolis police officer Mohamed Noor of third-degree murder and second-degree manslaughter is believed to be the first time in state history that a police officer was convicted of murder for an on-duty killing.

On Friday, Hennepin County Attorney Mike Freeman announced filing the same charges against former Minneapolis police officer Derek Chauvin in the death of George Floyd.

In doing so, Freeman once again finds himself in the glare of the national spotlight as he attempts to succeed a second time at what has been an exceedingly rare result in Minnesota and across the country — convincing a jury to convict a police officer of murder.

Despite what the now-viral video shows — a seemingly nonchalant Chauvin's knee pressing the neck of a clearly distressed Floyd for nearly nine minutes — local legal experts say convictions are far from ensured in cases where cops are charged with murder. Even when much of the public is convinced police were in the wrong, police officers have won acquittal.

From Freddie Gray's 2015 death in Baltimore while in police custody to the 2016 shooting death of Philando Castile during a Falcon Heights traffic stop, cases that seem open and shut often are not.

In part, it's because state law gives police wide latitude in using deadly force if they fear they or others will be seriously injured or killed.

While that seems unlikely from the video of Chauvin restraining Floyd, former Ramsey County Attorney Susan Gaertner said the fact remains that prosecutors must be painstakingly thorough.

"These cases are way more complicated and the burden on the prosecution is higher than I think the public understands," she said.

Thomas Heffelfinger, former U.S. attorney for Minnesota, agrees.

"It's not a slam dunk and these cases never are," Heffelfinger said. "These cases are hard to prove and we have to make sure we do it correctly."

Obtaining a murder conviction is not the only challenge Freeman faces.

Demands are growing louder for charges to be brought against the other three police officers who assisted Chauvin in restraining Floyd on Memorial Day. And the longtime prosecutor's relationship with the local black community continues to be strained.

In 2016, Freeman announced he was eliminating the long-standing and secret use of a grand jury in police-involved shootings after the November 2015 death of Jamar Clark. Activists praised the decision, only to make him the target of derision after he announced that he wouldn't charge the officers involved.

He faced a similar backlash in July 2018 when he declined to prosecute the officers involved in the shooting of Thurman Blevins, a decision made just one month after the shooting. And when Noor shot and killed Justine Ruszczyk Damond after he responded to her 911 call in 2017, some activists noted that it only occurred when the officer was black and the victim a white woman.

Freeman also drew controversy in the case when he was caught on tape telling activists before Noor's charging that he didn't have the evidence to do so because investigators "haven't done their job" and that a charge would be "the big present I'd like to see under the Christmas tree."

On Thursday, the county attorney was criticized after he said: "It's a violation of my ethics to talk about and evaluate evidence before a charging decision and I will not do that. I will say this: that that video is graphic and horrific and terrible and no person should do that. But my job in the end is to prove that [Chauvin] violated criminal statute."

Freeman later issued a statement "that it is critical to review all the evidence because at the time of trial, invariably, all that information will be used."

A group of local activists on Friday launched a campaign to remove Freeman from office, saying Freeman's statements Thursday "will make securing a criminal conviction against Derek Chauvin more difficult." The recall group said Freeman "has mishandled the murder of George Floyd" and that "this is not the first time that Mike Freeman has protected killer cops and stood in the way of justice for unarmed Black men. We cannot let him continue to use his office to protect police who abuse and murder Black and Brown folks in our city."

Even the charges Freeman chose to file against Chauvin — the same that were used to convict Noor — were criticized by local experts as understating the severity of the crime. In separate interviews Friday, local attorneys Joe Friedberg and Christopher Madel called Freeman's decisionmaking in the case "inexplicable."

"This doesn't make any sense. It doesn't fit this," Friedberg said of the charge of third-degree murder.

"That charge is more appropriate for someone doing something deadly, without a particular person in mind."

He added: "They have put themselves in a position here where any intelligent judge would dismiss this case."

Madel, a former trial attorney with the U.S. Justice Department who has represented clients in several high-profile cases, said the video of the incident appears to make a charge of second-degree murder more appropriate.

In the video, Chauvin appears to repeatedly ignore Floyd's cries that he can't breathe, despite witnesses pleading with him to stop.

"Multiple witnesses can be heard telling [Chauvin] 'I think you're killing him.' " Madel said. "And he just sits there with his hands in his pockets."

Despite the criticisms and challenges, Freeman on Friday appeared undaunted.

He touted the speed in which the charges against Chauvin were filed — less than four days from Floyd's death — as the fastest his office has ever brought charges against a police officer.

"This case has moved with extraordinary speed," Freeman said. "We have charged this case as quickly as admissible evidence has been collected and presented to us. We have now been able to put together the evidence that we need,"

And, for now at least, he said the third-degree murder charge is most appropriate. Freeman acknowledged the road ahead might be difficult.

The burden of proof makes it difficult to convict a police officer of murder. But, he reminded people Friday, his office has done it before.

And he seemed confident it would again, saying: "We have a very veteran prosecutor group, aided by a very veteran investigator group at the BCA [Minnesota Bureau of Criminal Apprehension]."