Ask a legal expert how tough it is to get a conviction against a police officer charged with fatally shooting someone in the line of duty and there’s a good chance they’ll point you to the case of Walter Scott.

The 50-year-old black motorist was shot in the back five times by a South Carolina police officer as he fled a traffic stop in April 2015.

It was captured on graphic video and viewed across the country:

State authorities in South Carolina swiftly charged officer Michael Slager with murder. His police chief said the footage “sickened” him. Then South Carolina Governor Nikki Haley called the conduct “not acceptable.”

Slager maintained during his 2016 trial that he shot out of fear for his life after Scott, who was unarmed, grabbed for his Taser.

RELATED: The latest updates from the Philando Castile shooting trial

After almost a day of deliberation, the jury announced it couldn’t reach a verdict, leading to a mistrial.

“There you had cellphone video of a police officer shooting a guy multiple times in the back as he ran away… and they still had a hung jury. When you can’t even get a conviction in a case like that, it just shows you how tough it is,” said David Harris, a University of Pittsburgh law professor and expert in police use of force.

It’s a case experts routinely cited when asked to describe the challenge prosecutors face as they seek a conviction in the case against the St. Anthony police officer accused of recklessly shooting and killing Philando Castile during a traffic stop last summer.

The trial of officer Jeronimo Yanez will open in Ramsey County on Tuesday, reigniting scrutiny of the seconds that preceded Yanez’s decision to shoot the 32-year-old black man shortly after pulling him over.

The incident’s aftermath was live-streamed on Facebook by Castile’s girlfriend, Diamond Reynolds, who was with him in the car at the time, as was her then-4-year-old daughter. The footage fueled protests locally and nationally about officers’ use of force against black men.

Following months of investigation, the 29-year-old Latino officer was charged by the Ramsey County attorney’s office with second-degree manslaughter and two felony-level counts of dangerous discharge of a firearm. The decision stunned many as Yanez is the first Minnesota officer in modern memory to be charged in such an incident.

He joins a small pool of officers who have been charged across the country in similar incidents.

While thousands of police have fatally shot someone on the job since 2005, only 81 have been charged with murder or manslaughter, said Philip M. Stinson, a criminologist at Bowling Green State University in Ohio who studies arrests of police. He previously worked as a police officer in New Hampshire.

And of those charged, anecdotal evidence suggests that the majority don’t end up being convicted, particularly if the officer takes the stand in his or her own defense, Stinson said.

“It’s very difficult to win these cases,” said Harris, the police use-of-force expert. “You have to have extremely strong facts of which there is almost no other explanation. … Even then, you still have so much to overcome.”

“Exhibit A is Michael Slager,” Harris continued.

After a jury couldn’t reach a verdict in Slager’s murder case, the officer pleaded guilty to a federal civil rights violation.

A particularly steep hurdle for prosecutors in all officer-involved shootings, Harris said, is convincing jurors to abandon the benefit of the doubt many instinctively give to police, who are legally allowed to use deadly force when facing a threat of serious harm or death to themselves or someone else.

“You have… a police officer who not all, but most, jurors are accustomed to seeing as the good guy, the person who you would call in trouble, the person you naturally believe, and now that person is in the defendant’s chair,” Harris said. “So just from the jump you are asking the jury to turn their world upside down.”

THE TRAFFIC STOP

Yanez was on patrol in Falcon Heights on July 6 when he decided to pull Castile over just after 9 p.m. He told his partner via radio that he was making the stop because the people in the car resembled suspects in a recent armed robbery in the area, according to the criminal complaint.

RELATED: Philando Castile case: A timeline

He added that “the driver looks more like one of our suspects just because of the wide-set nose.”

He also said the vehicle had a broken taillight, so he had a legal reason to make the stop.

The complaint cites audio and video captured from Yanez’s squad as the source for the previous quote as well as the following narrative:

At 9:04 p.m. Yanez turned on his squad lights and pulled Castile over. He walked up to the driver’s side of the vehicle. His partner went to the passenger side. Yanez proceeded to ask Castile for his license and proof of insurance.

After handing over his insurance, Castile told the officer, “Sir, I have to tell you that I do have a firearm on me.”

Yanez replied,“OK, don’t reach for it, then.”

Castile then said something inaudible on the recording, prompting Yanez to interrupt him and say, “Don’t pull it out.”

“I’m not pulling it out,” Castile responded.

Then Yanez screamed, “Don’t pull it out,” before drawing his own gun and firing seven shots into the vehicle. Five struck Castile.

The exchange lasted less than a minute.

Castile’s last words were “I wasn’t reaching for it.”

RELATED: Philando Castile case: A list of who’s who

Reynolds recorded on her cellphone what happened next. The footage shows Castile slumped over in the vehicle, blood staining his white T-shirt.

She and Yanez are overheard talking, with Yanez yelling repeatedly that he’d told Castile not to reach for it.

“You told him to get his ID, sir, and his driver’s license. Oh, my God, please don’t tell me he’s dead,” Reynolds said.

Castile’s handgun was found at the scene inside his pocket. His wallet, which contained his ID and license-to-carry permit, was also discovered in a pocket.

WHERE WILL THE CASE TURN?

Reynolds’ video has been viewed widely, but footage captured on Yanez’s dashcam will be played for the public for the first time at trial.

Even with that evidence, there is disagreement between the two sides about what happened in the seconds before the shooting.

The defense says that Castile was reaching for his gun and Yanez actually saw the firearm before shooting out of fear for his life. The state maintains Castile was trying to follow Yanez’s orders to produce his license when the officer recklessly fired.

That is where the case will likely “turn,” said John Arechigo, a criminal defense attorney who practices in downtown St. Paul.

“It’s going to come down to whether it’s believable that Philando Castile was actually reaching for his weapon and whether Officer Yanez actually saw it,” Arechigo said. “It’s not clear to the public yet … what exactly was going on in the car, and so far all we’ve heard is conflicting reports. … Hopefully some of that will become clearer in testimony.”

That adds weight to testimony both Reynolds and Yanez might provide at trial, and to the perceived credibility of each by the jury.

While the defense has not indicated whether Yanez will take the stand, legal experts say it’s likely that he will, given the nature of the case.

“Ultimately the prosecution is going to put out one version of events that will be backed up by Diamond, and the defense will present another based on Yanez, and the jury will have to decide who they believe,” said Ted Sampsell-Jones, a legal professor at Mitchell Hamline School of Law. “The jury is going to want to hear from him.”

Reynolds’ video, he said, could add to her credibility as she appears composed in the footage, whereas Yanez seems “out of control and panicked,” Sampsell-Jones said.

PROSECUTION’S TASK

Still, it will be difficult for the prosecution to try to discredit Yanez, a four-year veteran of the St. Anthony police department with no complaints in his personnel file, Sampsell-Jones said. Yanez is also married and has a young child.

“That’s a hard dynamic,” Sampsell-Jones said. “The prosecution is going to have to show to the jury, ‘Listen, I know you generally trust police officers, but this one is not telling the truth.”

Results of other cases across the nation shed light on how hard that can be, Stinson said.

While placing a defendant on the stand comes with risks, he said anecdotal evidence indicates officers who testify in their own trial tend to avoid conviction.

Ultimately, the state will have to prove that a reasonable officer in Yanez’s position would not have fired at Castile, Stinson said.

“Even if (Yanez) subjectively strongly perceived a threat, but a reasonable officer would not have perceived that threat, then (the shooting) is not legally justified,” Stinson said. “Jurors have trouble applying that standard though. … They think, ‘Wait a minute, the officer felt his life was in danger and here we have a man with a gun. I’m not going to convict that man.”

Working for the prosecution is the fact that there is audio and video of the event, as well as another witness, Reynolds, who can describe what happened, experts said.

They added that Castile’s disclosure of his firearm is also a plus.

“That idea that (Castile) would tell (Yanez) that but then make an effort to pull it out and use it on the officer when the officer had his insurance card … that will be really tough for the defense to deal with,” Harris said.

DEFENSE’S TASK

The presence of a gun could also help the defense, legal experts say, in the sense that it could have reasonably added to Yanez’s fear.

It was the gun and Castile’s decision to reach for it, Yanez’s attorneys have argued, that compelled him to shoot.

Since it’s the prosecution’s job to prove its case beyond a reasonable doubt, the only responsibility that falls to the defense is to create doubt, experts said.

To do that, defense teams sometimes try to disparage a victim’s character or that of key witnesses. Depending on the rules of evidence and the circumstances of each case, that could include bringing up past criminal convictions or drug or alcohol use.

In Castile’s case, the defense has already indicated it plans to address Castile’s marijuana use.

Since THC — a compound in marijuana — was found in his system, Yanez’s attorneys have said Castile was high at the time of the shooting and was therefore culpable in his death.

Harris called any plan to blame THC in Castile’s system for what happened “a red herring,” but Sampsell-Jones said the defense is duty bound to pursue what’s in the best interest of defendants.

“If (Yanez’s attorneys) feel impairment is an issue the jury should consider, then they have an obligation to present that,” he said.

YANEZ’S CASE IS UNIQUE

Among cases of officer-involved-shootings that have broken into the public’s awareness in recent years, there are elements of Yanez’s case that make it unique.

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“I found that video among all the others to be among the most painful … just because you see this man die in front of the face of his loved one,” Harris said. “We also know he was a law-abiding guy. … People loved him. … That just brings the whole thing home in a painful and sharp way.”

The fact that no confrontation between Yanez and Castile preceded the shooting also makes it stand apart, experts said.

There were also others at the scene, including Reynolds, her young daughter and Yanez’s partner, Joseph Kauser.

Nuances make up every officer-involved shooting, legal experts say, making it difficult to predict what will happen in Yanez’s case based on past criminal proceedings, especially considering the small sample size available for comparison.

“It’s going to be a tough case for both sides,” predicted Sampsell-Jones. “It’s not going to be a slam dunk either way.”