The law professor had one main message for prosecutors when he came to town: You shouldn’t always believe your eyes.

As the Jacksonville Sheriff’s Office and the police union hammer out details to implement body-worn cameras, prosecutors took an afternoon last week to learn how to use that evidence in court.

“As a prosecutor, any time we can have video footage of significant events in a criminal action it’s essential for us,” Chief Assistant State Attorney Mac Heavener said before the training. “The jury essentially becomes a witness to the things that happened.”

But then Seth Stoughton, a University of South Carolina law professor and one of the foremost body camera experts, raised his hand to interject. “Actually, I’m going to spend time this afternoon about why that’s not true.”

Last summer, the Jacksonville Sheriff’s Office began a pilot program with three different body-camera companies, allowing the same 30 officers to try the different technologies and assess which fits best. The office will begin the bidding process this summer to purchase office-wide cameras, spokesman Officer Christian Hancock said last month.

Stoughton came to Jacksonville to show prosecutors some of the limitations and biases of cameras, even as they may increase conviction rates. The cameras are tools, he said, and communities need to be careful before assuming they will act as a panacea. He told the prosecutors they should think about the kind of expert witnesses who can put the camera footage in perspective — technical experts, cognitive psychologists, vision scientists.

“When we’re talking about body-worn cameras as evidence, there are cases where it will help, cases it obviously won’t help, then cases where it looks like it will help but it actually hinders or harms.” He said the cameras could even potentially result in wrongful convictions or acquittals.

Camera footage can actually mislead, he said, making it look like something happened just because of the distortion of the camera or the angle. He showed the prosecutors a series of videos where an officer’s use-of-force might have appeared warranted on footage. Then he showed the same situations from a different angle.

Stoughton has prepared a similar quiz for The New York Times. Body cameras tend to make situations appear more intense and aggressive, he said.

State Attorney Melissa Nelson said introducing regular training sessions was a priority for her first year. The all-staff trainings have included legal writing, forensic science and cold-case investigations.

As part of those trainings, Stoughton urged caution before blindly trusting body-worn camera footage.

The union and the city have been debating the policies overseeing the body-worn cameras. The police union would like to keep the cameras on longer, while the city said it wanted the cameras turned off in certain situations where privacy might be a concern.

A few years ago, the conversations about body cameras centered around police accountability in the wake of officer shootings. But as the cameras have been implemented, they are much more likely to be used to gather evidence in everyday cases.

This has been one of the ways the issue of body cameras has evolved, Stoughton said. A few years ago, community activists seemed to want body cameras universally, while police departments seemed more skeptical. Today, both sides have more nuanced views of the cameras.

Michael Sampson, one community activist calling for more accountability over police, said that body cameras were never going to be the solution activists like him wanted. The cameras mean police are under more surveillance, but it also means the community is under that surveillance, too. “It’s not like the community wins with body cams. It’s more nuanced.

“It can go both ways. … It all depends on the prosecutor and how they choose to use that evidence.”

For example, the five anti-war protesters who were arrested in Hemming Park last year when their protest was disrupted by a Trump supporter later had their convictions withheld in part because of the overwhelming amount of cell phone footage that largely served to exonerate them. Yet those protesters didn’t see police, who used force to take down four of those protesters, arrested, either.

At one point, footage showed what looked like a stun gun being pressed into the back of a protester and the protester responding in pain. But Sheriff’s Office records said that officer’s Taser gun was never discharged.

It makes sense that cameras would benefit police and prosecutors day to day. The vast majority of arrests and stops aren’t going to lead to accusations of police abuse.

A national survey last year found that “nearly all prosecutors’ offices in jurisdictions” with the cameras have used footage to prosecute private citizens, compared to 8.3 percent of offices that have used them to prosecute police officers.

George Mason University’s Center for Evidence-Based Crime Policy’s report also said prosecutors overwhelmingly support the use of cameras, with a majority saying it would benefit the prosecution more than the defense. The cameras do, prosecutors said, increase their workload and their obligations to release evidence to the defense.

Stoughton praised Nelson for implementing regular training like this. “It’s so important. I may be biased since I’m in the education field, but constantly educating is the dream. The world is always changing. You can’t be complacent because if you ever take your education for granted you’ll get outpaced.

“I think if we jump forward 5 years I think a lot of agencies are going to adopt body-worn cameras, but I think a lot who are adopting them now will not be using them.”

Cameras, he said, are never foolproof.

In fact, the State Attorney’s Office tried to record Stoughton’s talk, but only after did an employee realize no one hit record.