Charges brought against police officers in fatal shooting incidents have spiked this year, but despite unprecedented scrutiny on police use of deadly force, researchers are reluctant to suggest an era of heightened police accountability is dawning.

A dozen officers have been charged in fatal shootings this year – the highest number in at least a decade – though data suggest there have been about 800 fatal police shootings this year. During the past decade, less than 1 in 4 of such prosecutions have resulted in convictions.

None of the officers charged this year have been convicted, but the number of prosecutions is up from an average of about five prosecutions a year from 2005-14, according to Philip Stinson, an associate professor of criminology at Bowling Green State University in Ohio, who has been tracking arrests and prosecutions of police officers for more than a decade.

Professor Stinson's research, which doesn’t include the six Baltimore officers facing charges in the death of Freddie Gray earlier this year, is part of a report he is preparing for the United States Department of Justice on police crimes and arrests.

Stinson – a cop-turned-lawyer-turned-criminologist – has been collecting data on police crimes and prosecutions since 2005, when he was doing his master’s degree at West Chester University in Philadelphia.

"We were in class and the issue came up. Somebody said, 'Cops don’t get arrested much,' and I thought, 'That's ridiculous. They do,' " recalls Stinson.

It was then that he began producing his own statistics, using 48 Google Alert search terms to drive his data collection. He wrote his PhD dissertation on data he collected from 2005-07. Since then, he has used grant money to further refine his methods at Bowling Green.

At a time when statistics on police crime were elusive, he became a trusted voice for government officials and reporters alike looking for concrete data on policing trends.

'Let's wait and see'

But his latest discovery – that police officers are being prosecuted this year at a rate more than double the average for the past decade – still leaves him skeptical.

He voiced some dissatisfaction, for example, with one headline on his research, which described a "surge" in police prosecutions.

"The numbers are so small I wouldn't read anything into it," he says. "It's not a statistically significant change because it's such a small sample."

He pointed to 2011, when there were seven officer prosecutions, the majority coming from two major incidents, including one in Atlanta where three officers were charged, and convicted, for fatally shooting a 92-year-old woman in her home during a botched drug raid.

"We've had 12 this year, OK. Let's see what happens over the next five years and see if we have a trend," he adds. "It could be an anomaly. It could be a pattern."

One trend that appears to be consistent is that it is still very difficult for a prosecutor to prove that an officer's use of force wasn’t justified. None of the officers charged this year have been convicted, and Stinson points out that of 47 officers who were charged from 2005 through 2014 only 11 were convicted, a rate of 23 percent.

In two of the most controversial use-of-force cases recently – the deaths of Michael Brown in Ferguson, Mo., and Eric Garner in New York – both officers at the center of the incidents were acquitted by grand juries. In one recent case out of Cleveland that went to trial, a dozen officers fired 137 bullets into a car, killing the two occupants after a high-speed chase. Only one officer was charged, and a judge found him not guilty.

Kami Chavis-Simmons, a former US attorney who now directs the criminal justice program at Wake Forest University School of Law in Winston-Salem, N.C., says that prosecutors still face "a pretty high burden" of proof that the officer’s use of force was unreasonable – particularly given that judges and juries tend to be sympathetic to the officer, who was most likely "in dangerous situation, having to make a quick decision."

"Even if you have an increase in the indictments or prosecutions, that does not necessarily mean that you have an increase in the number of convictions," she adds.

But there's a chance the spike in officer prosecutions could persist, experts say, in part because of public pressure and video technology.

The prime example is the prosecution of Michael Slager, a former officer in North Charleston, S.C. Mr. Slager is accused of fatally shooting Walter Scott earlier this year after a traffic stop spiraled out of control. Investigators accepted Slager's initial report – that Mr. Scott had attacked him and taken his Taser – until a few days later, when a bystander video surfaced. Slager was promptly fired and faces a murder charge.

“When you have that type of objective evidence it might be enough to initiate a prosecution," says Dr. Chavis-Simmons, "where before we might just have the officers – particularly if it's a death and there are no witnesses – we just have the officer's rendition of what happened."

More data needed

What all experts agree on is that there is a need for more data on policing generally, and police use-of-force specifically. At the moment, some of the best databases are being maintained by news organizations like The Washington Post (814 shootings) and The Guardian (940 deaths). The Post and the Justice Department have approached Stinson about using his data, which is something he never would have anticipated when he created those first Google Alerts 10 years ago.

"When I started this I was worried people would critique the rigor of my methodology," he says.

Even now, with his data among the most trusted in the country, he admits it’s still not enough. "We don’t pretend to capture everything," he says.

And a comprehensive national database could be invaluable in identifying how and when police use deadly force, says Chavis-Simmons. It can also signal what departments are "doing well that other jurisdictions can learn from."