Is violence contagious? A recent spate of incidents in both Colorado and Maryland suggests that bad things tend to happen in clumps, a syndrome that psychologists have known about for decades.
At-risk individuals, the young males who commit these violent events, may see something in the media and brood about it, according to Edwin Megargee, professor emeritus of psychology at Florida State University.
The media exposure "can shape the form in which the violence may take place," he said. "People get the idea and maybe start obsessing."
In the suburbs around Denver, recent acts of violence have gotten some people thinking that there may be something like a contagion underway. On Monday morning, a 16-year old student in Westminster, Colo., walked into the cafeteria at Standley Lake High School, set himself on fire, injuring two classmates. He is in critical condition at a hospital and police say he was trying to commit suicide.
Westminster is the same place where in 2012, 17-year-old Austin Sigg kidnapped and killed a 10-year-old girl, Jessica Ridgeway.
On Jan. 23, Columbine High School, where two former students killed 13 people in 1999, went on alert after receiving threatening phone calls. Authorities applied the alert to several other schools in the area, including Standley Lake, according to the Associated Press.
On Dec. 13, student gunman Karl Pierson, 17, fatally shot Claire Davis, a 17-year-old classmate at Arapahoe High School in nearby Centennial, Colo., before killing himself in the school's library. Pierson reportedly had threatened a teacher and librarian who had disciplined him last year and allegedly was seeking that teacher when he entered the school, investigators have said.
In Columbia, Md., on Jan. 25, a 19-year old man opened fire with a shotgun in a mall, killing two employees at a skateboard store. He then committed suicide. Two days later, a 31-year-old man was arrested at another Maryland mall for threatening to kill employees of a luggage store.
"It's called the bandwagon effect," said James Janik, chief psychologist at the Cook County (Ill.) Juvenile Detention Center. "Any kind of behavior that happens around you, you are apt to increase."
Janik said that the common thread among many young people who resort to violence is a feeling that they can't figure out a solution to their problems.
"If you haven't had a lot of both exposure to problem-solving situations or skills that aid with seeing a lot of possibilities, you begin to get insular, you stop looking at possible solutions," Janik said. "There's a phrase that violence is the common pathway and a simple solution. If you see that as your only alternative, you have no other skills, you're going to try that out."
On expert cautions that violence has many roots, and that copycat behavior doesn't explain everything.
"It seems unlikely that someone who is not predisposed to commit a violent act is watching TV at home and says I'd like to do this too," said Laurence Steinberg, author of the upcoming book "Age of Opportunity: Revelations From the New Science of Adolescence." "But someone who is already angry and has a reason to commit an act of violence but hasn't settled on a plan, sees or hears some other act, and maybe says 'I'm going to do that too.'"
Steinberg noted the relative ease of obtaining weapons has made committing violence against others easier than ever before.
"You've got this toxic mix of mental illness and access to firearms," he said. Everyone agrees it's a bad combination."