Murders inspired by 'The Purge'? Mass shooting stirs public concern.

A trio of murders in Indiana may have been inspired by a 2013 Hollywood movie depicting random violence – and the news is raising anew troubling questions about how America should grapple with the problem of mass shootings.

Prosecutors have filed court documents charging Johnathon Cruz, a 19-year-old Indiana man, with randomly killing three people as part of a four-day crime spree. The documents allege that the killings were modeled on the film “The Purge.”

In the fiction movie, the federal government enacts a 12-hour period during which all crimes, including murder, are legal.

The court documents, filed Wednesday prior to an initial hearing for Mr. Cruz on Thursday, allege that he killed Billy Boyd and Jay Higginbotham on May 12 and Jose Alberto Ruiz on May 15. Cruz is charged with three counts of murder as well as other felonies.

The apparently senseless nature of the killings has stirred public shock but also may add to the urgency of national debate over preventing such incidents.

"Just when you think you can't experience anything more inexplicable and shocking, as we frequently do, you are then confronted with circumstances that almost leave you at a loss for words," Marion County Prosecutor Terry Curry said of the attacks.

The Indiana case follows other high-profile mass killings in recent years that happen to involve young, white men with access to guns.

The list includes Dylann Roof in the 2015 Charleston, S.C., church shooting; Adam Lanza in the 2012 Sandy Hook elementary shooting in Connecticut; and James Holmes in the Aurora movie theater shooting in Colorado. Yet, although surface motives may be apparent in the case of such killings – Roof’s hatred of blacks or Cruz’s apparent infatuation with “purging” – experts say there is no simple answer as to why some turn such thoughts into tragic actions.

"There are pieces of the puzzle, and you put them all on the jigsaw board, and you're still going to have a big hole there,” Jeffrey Swanson, professor in psychiatry and behavioral sciences at Duke University told CNN after the Dylan Roof incident in South Carolina last year.

“What I do know is that violent behavior – whether it's serious violence or minor violence in populations – is never just one thing. It's not a one thing problem. It's going to be an accumulation of things, kind of a whole cocktail of factors," he said.

Among those puzzle pieces, three in particular have drawn attention – race, gender and mental illness.

A CNN analysis of data on mass shootings since 1984, compiled by Mother Jones, found that white men were perpetrators in most cases (63 percent), blacks in 16 percent, of cases, and Asians in 9 percent of cases. When those numbers were adjusted proportionately to population size, blacks and whites committed such crimes at roughly similar rates, while Asians were overrepresented as perpetrators and Latinos were underrepresented.

The analysis also said men commit about 90 percent of all murders and, relatedly, that they are more likely than women to own guns.

It also quoted research finding that a majority of mass shootings between 1915 and 2013 were carried out by individuals with a mental illness.

The hard-to-predict nature of those who become mass shooters has been at the heart of America’s heated gun control debate.

President Obama in January issued an executive action outlining, among other measures, controversial background checks and stronger policing of gun sales. Democratic front-runner Hillary Clinton has said she would go further. The backlash from Second-Amendment advocates and the gun lobby has been fierce.

The news of the Cruz case followed on the heels of the what police believe was a premeditated murder-suicide by a former University of California, Los Angeles student against a professor.

Today, National Gun Violence Awareness Day, has been bookended by the headline-making gun violence.

Former Democratic Rep. Gabby Giffords of Arizona, who survived an assassination attempt in 2011, wrote a Vogue op-ed to mark the day.

“Gun violence is a full-blown national crisis – one that, on an average day, claims 91 American lives, including seven children and teens,” she wrote.

There were a total of 53,254 shootings (13,243 deaths) in 2015, according to The Gun Violence Archive. So far this year there have been 21,684 shootings (5,981 deaths).