In this Tuesday, July 28, 2015 file photo, mourner JeRee Wilson holds her fist in the air outside funeral services for Samuel Dubose at the Church of the Living God in the Avondale neighborhood of Cincinnati. Dubose was fatally shot by a University of Cincinnati police officer who stopped him for a missing license plate. Volatile, racially sensitive questions of whether to charge police officers for fatal on-duty shootings, and whether jurors will convict an officer in such a case, hang over two of Ohio's largest cities. (AP Photo/John Minchillo, File)
In this Tuesday, July 28, 2015 file photo, mourner JeRee Wilson holds her fist in the air outside funeral services for Samuel Dubose at the Church of the Living God in the Avondale neighborhood of Cincinnati. Dubose was fatally shot by a University of Cincinnati police officer who stopped him for a missing license plate. Volatile, racially sensitive questions of whether to charge police officers for fatal on-duty shootings, and whether jurors will convict an officer in such a case, hang over two of Ohio’s largest cities. (AP Photo/John Minchillo, File)

Volatile, racially sensitive questions of whether to charge police officers for fatal on-duty shootings, and whether jurors will convict an officer in such a case, hang over two of Ohio’s largest cities.

A Hamilton County judge is expected in February to set a trial date for a former University of Cincinnati police officer charged with murder in the fatal shooting of an unarmed black motorist after a traffic stop. Meanwhile, a Cuyahoga County grand jury has been hearing testimony about potential charges in the Cleveland police killing of a 12-year-old black boy who had a pellet gun.

The cases come during heightened scrutiny across the United States of police treatment of blacks, after a string of police-inflicted deaths from Ferguson, Missouri, to Chicago sparked sometimes-violent protests over the past 16 months. Cleveland police arrested more than 70 people in May during protests after a judge found Patrolman Michael Brelo not guilty of voluntary manslaughter in the November 2012 deaths of two unarmed motorists in a 137-shot barrage of police gunfire after a high-speed chase.

They also come after a year in which the number of U.S. police officers charged in on-duty shootings was triple the average, according to Philip Stinson, a Bowling Green State University criminologist who tracks charges against police. A Chicago police officer charged last month with murder in a fatal shooting was at least the 15th such case this year, compared with an average of fewer than five a year, Stinson said recently.

Michael Benza, a criminal law professor at Case Western Reserve University in Cleveland, said that accompanying the increased attention to such cases is an erosion of public faith in police credibility.

 In this Saturday, May 23, 2015 photo, mounted police officers follow demonstrators as they march through downtown during a protest against the acquittal of Michael Brelo, a patrolman charged in the shooting deaths of two unarmed suspects, in Cleveland. Brelo was acquitted Saturday in a case involving a 137-shot barrage of gunfire. Volatile, racially sensitive questions of whether to charge police officers for fatal on-duty shootings, and whether jurors will convict an officer in such a case, hang over two of Ohio's largest cities. (AP Photo/John Minchillo, File)
In this Saturday, May 23, 2015 photo, mounted police officers follow demonstrators as they march through downtown during a protest against the acquittal of Michael Brelo, a patrolman charged in the shooting deaths of two unarmed suspects, in Cleveland. Brelo was acquitted Saturday in a case involving a 137-shot barrage of gunfire. Volatile, racially sensitive questions of whether to charge police officers for fatal on-duty shootings, and whether jurors will convict an officer in such a case, hang over two of Ohio’s largest cities. (AP Photo/John Minchillo, File)

“That’s the real problem,” he said.

The widening availability of video — from police dashboard cameras, police body cameras and citizens’ smartphones — has played a role in the increased number of charges. Stinson reported that 10 of this year’s 15 cases involved video.

But even with video, officers’ actions can be subject to interpretation.

“The biggest argument that law enforcement uses, and which the law recognizes, is that officers have to make these decisions instantaneously in many of these cases,” Benza said. “Usually it’s in this high-tension, high-adrenaline moment … ‘Do I shoot or do I not?’ It’s easy afterward to sit down and calmly look at the video and come to the decision. The officer doesn’t have that luxury.”

In the Cleveland case of the November 2014 shooting of 12-year-old Tamir Rice, experts hired by prosecutors concluded that the use of deadly force was justified because the officers didn’t know the boy was holding a replica gun that shot plastic pellets.

In this Saturday, May 23, 2015, file photo, demonstrators pause to stand in solidarity during a protest against the acquittal of Michael Brelo, a patrolman charged in the shooting deaths of two unarmed suspects in Cleveland. Brelo was acquitted Saturday in a case involving a 137-shot barrage of gunfire. Volatile, racially sensitive questions of whether to charge police officers for fatal on-duty shootings, and whether jurors will convict an officer in such a case, hang over two of Ohio's largest cities. (AP Photo/John Minchillo, File)
In this Saturday, May 23, 2015, file photo, demonstrators pause to stand in solidarity during a protest against the acquittal of Michael Brelo, a patrolman charged in the shooting deaths of two unarmed suspects in Cleveland. Brelo was acquitted Saturday in a case involving a 137-shot barrage of gunfire. Volatile, racially sensitive questions of whether to charge police officers for fatal on-duty shootings, and whether jurors will convict an officer in such a case, hang over two of Ohio’s largest cities. (AP Photo/John Minchillo, File)

In the Cincinnati case, in which former UC officer Ray Tensing was charged in the July 19 shooting of Samuel DuBose, 43, after stopping him for a missing front license plate, his attorney has contended that Tensing feared he would dragged under the car when DuBose tried to drive away.

In both cases, the county prosecutors have been criticized, for very different reasons.

Attorneys for the Cleveland boy’s family wrote a Dec. 14 letter to the U.S. Justice Department complaining that Cuyahoga County Prosecutor Tim McGinty “has abdicated his responsibility to conduct a fair and impartial investigation and has severely compromised the grand jury process.”

In the Tensing case, Hamilton County Prosecutor Joe Deters’ acerbic commentary about the officer as he announced his indictment drew criticism and led to a pending request by defense attorney Stewart Mathews to move the trial to another county. Deters called Tensing’s decision to shoot “asinine” and “senseless” after a “chicken-crap” traffic stop.

 In this Friday, July 31, 2015 file photo, people chant, "hands up, don't shoot," to a Cincinnati Police Officer as they march along Sycamore Street during a vigil to honor Samuel DuBose in Cincinnati. Dubose was fatally shot by a University of Cincinnati police officer who stopped him for a missing license plate. Volatile, racially sensitive questions of whether to charge police officers for fatal on-duty shootings, and whether jurors will convict an officer in such a case, hang over two of Ohio's largest cities. (Cara Owsley/The Cincinnati Enquirer via AP, File)
In this Friday, July 31, 2015 file photo, people chant, “hands up, don’t shoot,” to a Cincinnati Police Officer as they march along Sycamore Street during a vigil to honor Samuel DuBose in Cincinnati. Dubose was fatally shot by a University of Cincinnati police officer who stopped him for a missing license plate. Volatile, racially sensitive questions of whether to charge police officers for fatal on-duty shootings, and whether jurors will convict an officer in such a case, hang over two of Ohio’s largest cities. (Cara Owsley/The Cincinnati Enquirer via AP, File)

Prosecutions that lead to police convictions have continued to be rare. Stinson found that of 47 police officers charged from 2005 to 2014, less than a fourth were convicted.

Benza said it’s too soon to say whether new trends are being established.

“Stay tuned, because it’s going to keep evolving,” he said.