People threatening to 'come back Orlando-style' highlights an unsettling side effect of gun violence

Ever since a gunman carried out the deadliest mass shooting in US history on Sunday, fears of a copycat have emerged.

"Sometime within the next two weeks, we're going to have another one of these incidents," Pete Klismet, a former hostage negotiator with the FBI, told a local Colorado news site. It's a "statistical reality," he added.

The Orlando shooter targeted Pulse, a gay nightclub in Orlando, killing at least 49 people.

Later that day, police arrested a man headed to the Los Angeles gay pride parade with guns and explosives in his car. Several days later, police arrested another man who threatened to "come back Orlando-style" during a fight with bouncers at a Brooklyn bar, the New York Daily News reported.

Recent research, combined with data from the Brady Campaign to Prevent Gun Violence and the FBI, suggests that mass shootings can lead to copycats and further perpetuate the violence.

Within 13 days, on average, the original incident is "contagious" and incites at least 30% of subsequent shootings, according to a study published in 2015 in the journal PLOS One. The effects apply to subsequent incidents within that time frame as well, spider-webbing the effects.

"The copycat phenomenon is real," Andre Simons of the FBI's Behavioral Analysis Unit told NBC, in regard to a 2014 FBI report about the prevalence of mass shootings. "As more and more notable and tragic events occur, we think we're seeing more compromised, marginalized individuals who are seeking inspiration from those past attacks."

The lead author of the study in PLOS One, Arizona State University professor Sherry Towers, said she sees a connection between copycats and the media's extensive coverage of gun violence.

"What we believe may be happening is national news media attention is like a 'vector' that reaches people who are vulnerable," she told CNN.

When coverage remains local, usually in cases when less than four people are killed, researchers didn't see the same contagious effects. Oppositely, when national media grabs onto the story, people - who may already have access to weapons - use the original shooting as inspiration.