In recent days, police have responded to active shooter incidents at an airport, a shopping mall and a school, highlighting the increased frequency of rampage attacks and the diversity of locations in which they occur.
While the violent crime rate is dropping nationally, the incidence of mass shooting events has sharply increased in the past recent years, according to a new study.
"We used to see an attack once every other month. Now we see more than one a month," said J. Pete Blair, a criminal justice professor at Texas State University who recently completed a study of the phenomenon. He defined an active shooter as an incident "in which someone goes somewhere with the intent or potential of committing mass murder, even if they don't kill anyone."
Before 2008, there were around seven events in any given year, according to Blair's research.
In 2010 a record-breaking 21 incidents took place. Another 11 were recorded in 2011, and 15 in 2012, Blair said.
"It's hard to say what's driving the increase. In some cases shooters are motivated by notoriety or fame. They see this as a way to become a recognize household name," Blair told ABCNews.com.
Blair, whose research is funded by the U.S. Department of Justice and the Texas Governor's Office, found that most mass shootings occurred where people spend most of their time – at work, and school.
Forty percent of events occur at businesses, 30 percent at schools (from kindergarten to universities,) 18 percent occurred in outdoor public places and 12 percent occurred in other locations.
Those other locations, which include places like shopping malls, movie theatres, churches and military bases, often garner the most headlines and potentially worry people the most, but are in reality the least common.
A survey by ABCNews.com of the 25 deadliest mass shootings in U.S. history, dating back to the 1966 University of Texas shooting, which killed 16, found that much like the active shooting events, most mass killings also occurred at workplaces or schools.
The latest active shooting event, which became a mass killing, occurred Friday at Los Angeles International Airport, in which one person was killed and three others were injured.