The mass killer of defenseless students and staff at a Newtown, Conn. elementary school last December was basically addicted to playing violent video games – and there are lingering questions if exposure to virtual violence could lead to later violent acts.

Long before the shooting, Adam Lanza spent many hours locked up in his house playing what CNN described as “military-style video games.” A search of his family’s house uncovered thousands of dollars’ worth of violent video games.

In fact, Lanza’s most popular game was reportedly “Call of Duty,” which recreates the violence found during World War II battles, The New York Daily News reported.

While it’s debatable if playing these games influenced his decision to undertake a shooting spree at the school, a new study from the University of Connecticut and Wake Forest is showing that violent video games could be connected to aggressive thoughts and speech.

But the researchers are quick to add the study shows there is no increase in physical aggression after playing video games with human looking characters.  Also, the researchers suspect human-looking characters in games “may be more likely to provoke violent thoughts and words than games where monstrous creatures are the enemy.”

“The research clearly suggests that, among other risk factors, exposure to violent video games can lead to aggression and other potentially harmful effects,” Kirstie Farrar, a  UConn professor and the lead researcher in the study, said in a university statement.

“The more human players perceived the aggressive targets to be, the more verbally aggressive they were and the more violent words they generated,” the study adds. “Although we predicted that less human targets would result in more aggression, players seemed to be more aggressive after perceiving more human targets.”

Violent video games represent just one risk factor in later aggressive behavior, the study suggests.

"It's one of many risk factors, but it is one that parents, for example, can exert some control over," Farrar explained to the Hartford Courant newspaper. "So, I think parents need to be aware of what some of this research is suggesting when they make their decisions about [whether] they're going to let their kids play these games."

There is also recent concern from several U.S. political leaders about the impact of violent games or other forms of violent entertainment on certain sectors of the public.

"The violence in the entertainment culture – particularly, with the extraordinary realism to video games, movies now, et cetera – does cause vulnerable young men to be more violent," former Sen. Joe Lieberman (I-Conn.) said in a statement.

There is also a question about the impact of violent games on those with some kind of mental or emotional challenges.

"There might well be some direct connection between people who have some mental instability and when they go over the edge – they transport themselves, they become part of one of those video games," Colorado Gov. John Hickenlooper added. It was Colorado where 12 people were killed in a movie theater shooting last year.