Long before James Holmes allegedly opened fire in a crowded Colorado movie theater, there was debate over whether violent movies spur violent acts. 

Dr. Jay Reeve, the president of a mental health facility in Florida, says it would be wrong to blame movies entirely.  Reeve, who has studied the effects of movies on behavior, says people predisposed to violence are attracted to violent movies.

"Folks are walking into these movie theaters with certain kinds of vulnerabilities, with a certain set for things and in a way, the movie just is another vehicle for them to express something that, you know, my guess is they would have expressed anyway," he said. 

Investigators said a teenager convicted in the Washington-area sniper shootings that killed 10 people in 2002 was fascinated by The Matrix, a science-fiction thriller.

John Hinckley, the man convicted in the 1981 attempted assassination of U.S. President Ronald Reagan, appears to have followed the plot from the movie Taxi Driver.

And in the aftermath of a 1999 mass shooting at Columbine High School in Colorado, investigators said one of the two teenaged gunmen had a journal reference to the Natural Born Killers movie.  Also, families of victims questioned whether both gunmen were influenced by The Basketball Diaries, another movie with graphic violence.

University of Michigan psychology professor Rowell Huesmann, says people can be influenced by a movie. "Violent movies can increase the risk of a person behaving violently," he said.

But he says a wide range of factors, such as mental health and aggression at home, have to be taken into consideration. "Yes, I would say violent movies, violent TV, violent video games do cause an increase in the risk of violence but it would be a mistake to think that by themselves these cause the violent acts.  It's usually they have to be combined with other psychological factors in the person," he said. 

Criminology professor James Fox at Northeastern University in Boston says most people have no problem separating fantasy from reality. "There are millions of people who are interested in, fascinated and sometimes even obsessed with violent entertainment and of course they don't go on rampages," he said. 

He says for some criminals, it could be that violent entertainment is a reflection of their personalities but not the cause of their actions.