A few days after Sandy Hook, Attorney General Eric Holder traveled to the site of the mass shooting, spoke with first responders and looked at the pictures.

“I was crying. It was without question the worst day that I had as attorney general, and maybe the worst day in my professional life,” Holder said.

Despite a major push, President Barack Obama was unable to win passage of any sort of legislation following the massacre that killed 20 children. But rather than better politics, or a less powerful lobbying industry, Holder believes one simple act could change that outcome.

“If the American people had access to those pictures, if the American people had seen those pictures [from the scene at Sandy Hook], the calls for reasonable gun safety measures would have been passed.” Holder continues. “And to see the innocence that created those pictures — about what they wanted to do in first grade that year, juxtaposed with the scene of carnage that you saw that was wreaked by [shooter Adam] Lanza. It was something that haunts me, that stays with me even now. I mean, as we’re talking about it, I can bring up the images in my mind too easily.”

It’s an interesting question: Would America have a different set of gun laws if graphic images of gun violence were circulated across TV screens and news websites?

Indeed, photographs have changed public opinion in significant ways. Iconic images of Vietnamese children running from napalm during the Vietnam War helped flame an anti-war movement. The mutilated body of Emmett Till fueled the Civil Rights movement. More recently, the photo of a young Syrian child, drowned and washed ashore on a beach in Turkey, altered the perception of the refugee and migrant crisis.

But Kimberly Rule, a former crime scene investigator and now a professor at George Mason University, says that there is a fine line between informing people to spark emotion, and causing trauma to viewers.

“I do not believe that it is appropriate for the public to view some of these graphic images,” says Rule, who saw thousands of gruesome images as a crime scene investigator. “These images, if they are shown, they need to be more probative than prejudicial. I think that’s the key, and not just to spark this type of emotion. Because I feel that could do some emotional and psychological damage to the average public member, who might not be able to have certain coping mechanisms.”

Even more damaging, Rule believes, is the potential impact on a victim’s family.

“It’s not to say that everything has to be shielded. I think maybe some images. But the really graphic ones, I think we need to be very very careful, and not only to protect the public, but also to protect the victim, and the victim’s family. I always have to think, ‘What if that was my child that was being displayed for everyone to see.’ What psychological impact would that have on the victim’s family and friends?”

But this emotional element is what is so key in changing opinion, says Liana Peter-Hagene, a researcher in the department of psychology at the University of Illinois at Chicago. Much of what she looks at is the emotional factors in jury decision making.

“I think that emotional photographs, especially graphic photographs, can definitely sway public opinion,” Peter-Hagene says. “Emotional evidence has a really strong effect on judgements and on attitudes.”

Not only can images change opinions, they are also important motivating factors for action to those that are already convinced of a certain opinion.

“Emotional evidence can also motivate people who are already in support of gun control to be more vocal and more firm in their support,” Peter-Hagene continues. “That’s another aspect that’s very important in the way that these pictures could affect public opinion and shape policy. It would make people who are passive but pro gun control more active and vocal, and motivated.”

Rule acknowledged that certain photographs should be shown, but worries that if the public is flooded by them, they might become desensitized.

Rule notes, “I would caution what images are shown, and who decides when is enough. Eventually you’re going to overwhelm the public with these images to the point where this can really start to backfire, because it’s going to start to desensitize the public.”

Even if potentially desensitizing, showing the public graphic photographs might mean very different policy results. Peter-Hagene points to the effect of the image of the drowned child on the Turkish shore, which shows just one victim, and one individual story.

“It’s not that graphic, but it’s very impactful. It speaks to the level of harm. It shows you a real victim, so it has a very strong emotional impact, without being disturbing in that very graphic way. And there’s also research that shows that people are more swayed by one example, one victim. It has more of an impact than 1,000 victims, when it becomes kind of like statistics.”